1) In the US in that time period there was no distinction between the guns found on the East Coast from those found on the West Coast. The then new US Highway system, rail traffic and air travel ensured that what a consumer could buy on one coast would also be available on the other coast. California's crazy laws were decades away.
2) You picked a pivotal decade. In many ways in the US the 1960s were just as turbulent as the 1860s. Up until 1968 in addition to standard civilian sporting weapons, any and just about all military surplus weapons (including cannon, bazookas and mortars) used by any participant of WW2 were available for quick purchase by mail in many magazines of the era. In the case of full-automatic weapons, such as Tommy guns, Sten guns, Browning machine guns, etc., Federal law back then merely required that the weapon was de-activated (dewat). The Dewat procedures varied depending on who was doing the dewat certification. In some cases merely filling an internal cavity with some molten lead, or applying a spot weld to a breach was considered sufficient. Obviously many, many, people did buy these dewat weapons, then with a little heat or a few minutes with a file or a chisel restore them to perfect function. Explosives were also very easy to obtain and many corner hardware stores carried both dynamite and surplus grenades. Quite literally the America of my youth was an armed camp waiting for the coming nuclear war and Soviet invasion. [Crazy men on both sides running military's and governments added to the anticipation.] On the West Coast there were a bunch of crazies running around with private volunteer armies, the Minutemen (they had tanks too), the John Birch Society, the KKK, and a long list of less well known groups.
[Even in NYC where I grew up, the Sullivan Law of the time did not prevent dewats (not that a mere law has ever prevented anything) and I knew 3 different households on my block alone where (no longer dewat) full auto weapons could be found. One quite illegal, but then easy to obtain Thompson was in the house of my Scoutmaster.]
Our military sold off surplus trucks, jeeps, tanks and bombers left over from the recent wars to anyone with the money to buy them. Several foreign coups attempted coups and revolutions used such surplused 'scrap' vehicles and munitions. The B-26 and B-25s were pretty popular purchases for those wishing to bomb a capital somewhere. Likewise many military C-47s were used to start small freight companies both in and out of the US.
In 1963 a nut assassinated a US President with a mail ordered surplus rifle. Another nut climbed a tall tower with an assortment of surplus military weaponry and sniped a dozen or so people out of existence. Those who stored explosives in their homes (along with their neighbors) sometimes learned the hard way why the military does not store explosives inside barracks buildings. The passage of the Civil Rights Act in '64 primed the stage for upheavals. Different elements of the populace had different personal interpretations of the Constitution. Riots and killings followed. When the US Attorney General was assassinated by another crazy, Congress with the consent of the NRA passed the Dodd Act in 1968. Suddenly all those dewat weapons and crates of hand grenades, and boxes of dynamite became illegal and subject to confiscation and destruction without compensation. There was a brief amnesty period and maybe a half million such weapons were handed in voluntarily. Others carefully hidden for decades still pop up now and then and someone usually goes to jail. Many military surplus pistols of other countries were now banned from importation. [This led to an increase in collector value for those that made it in before the deadline.] Previously it had been standard practice (subject to the approval of a base commander) for retiring officers and favored NCOs to purchase their sidearms. The weapon was declared unserviceable and sold as scrap by the base. Even if there was nothing wrong with it. Likewise, the US Post Office had hundreds of thousands of pistols stored there by the Military, which in the 1960s when the Post Office suddenly became an 'independent' corporation suddenly became their property and were promptly sold as surplus to department stores and other buyers. All of those government sales of surplus pistols, tanks, trucks and bombers were now stopped. Another side effect of the 1968 Dodd Act was that for the first time possession of a firearm by a convicted Felon or a person found by doctors to be insane was illegal. Previously felons released from jail would often make their first stop a pawn shop where they could quickly buy a new gun.
3) In the same time period there were some makers of cheap firearms. Back then a gun had to be pretty cheaply made to be economically competitive with a military surplussed .32 or a .380. Makers such as Clerke tried to fill this 'bottom rung of the ladder' economic nich. US Cadet revolver comes to mind. In places like NYC where handgun permits were either non-available or required a bribe to a precient Captain or a City Council member, certain brands of children's cap pistols or starter pistols were sold in hardware stores instead of toy stores, simply because converting them to cheap real pistols of low power (i.e., a .22) wasn't all that hard. New handgun design was otherwise pretty stagnant in the 1960s as the WW2 (and WWI) surplus pistols were being sold just about everywhere. Although Colt was rocking the boat with it's new AR-15/M-16 designs the rifle industry was also pretty much stagnant given the glut of surplus M-1s, Enfields, Ariskas and Mausers for sale filling the pages of the gun magazines of the era.
It mostly wasn't until the 1970s with the military surplus weapons no longer being cheaply available to the new buyers that the firearms industry began pushing new designs out the door.