C&R is curio and relic Federal Firearms License (FFL). That means from your perspective the gun is more than 50 years old and rare enough to be called a curio (such as a German Luger, a Colt peacemaker, an Ariska rifle, etc.). It allows you to acquire old broken guns across state lines and says you are a collector. You are not a dealer and the license does not allow you to sell guns as a business. Really IMO the only person you should ever sell a gun to is an FFL holder. Your drawback is unless you want ATF to come knocking on your door you bring the fixed guns to an FFL dealer and sell them to him. The C&R license is of no value to you whatsoever if you are looking for new guns. Alternatively, new guns, broken or not, are rarely placed for sale. They are usually just repaired. There is a whole forum here about C&R licenses and you should visit it.
BTW, learn what is junk (i.e., not worth the time and effort) and what isn't. Know your limitations. If the frame is damaged or it has been in a fire don't buy it. What you are looking for is old guns from major makers that just need a new spring or a small part. You will find some parts are almost impossible to find. If the part is easy to find, someone else would have already done the repair.
Forget about finding old Colt 1911s or Lugers with a broken part. It happens, but since the replacement parts can be quickly located on the Internet, it doesn't happen much. What you will mostly be locating is things like early Stevens .22 rifles with missing or broken firing pins, old Sears & Roebuck shotguns with broken stocks, Hopkins and Allen spur trigger revolvers with broken leaf springs, Spanish revolvers with broken hammer spurs or rusted frozen triggers, and stuff like that. Just about any major countries military weapons have plenty of parts easily available for them, so they probably won't go up for sale as a broken gun very often. If they do, something isn't right. A broken Mauser rifle, even one from WWI is pretty easy to find parts for, so the question becomes, what else is wrong? Etc.
I had to wait 20 years to locate missing parts for one gun (purchased at a pawn shop) which I eventually restored. You may also want to take some courses at your local community college and learn to run a lathe and a mill. I did. Learn about welding too is my suggestion. You will probably never want to weld anything, but it is a very good way to learn about the classes and different types of steel, other metals and the significance of heat treating. A firm called Micromark sells some pretty decent small (micro) mills and lathes that run off 110 volts. Buy those after you complete the courses, not before. Making new parts from scratch, out of the proper metal, is sometimes the only way to fix an old gun with a broken part (such as a trigger or a hammer spur).
Check out Brownells for tools and materials.