This is what yahoo pulled up, go to shotgunworld link that I have posted. I looked at an old link from Gunbroker they had 20 ga and 12 ga models.
Shotgunworld.com • View topic - BOST SxS Date?
Answers.com - Any info on a sxs 12 gauge made by armas bost eibar
BOST ARMAS EIBAR SPAIN
These Shotguns Are very Rare and are starting to get the attention from serious collectors.
Bost shotguns are Manufactured in Eibar Spain and are all hand made.
The scroll work on the metal and etching in the wood are done by hand and not stamped.
Not to be confused with Boss company of England.
There are five gun manufacturer's in the Basque town of Eibar Spain within walking distance of each other.
Most of the Bost rifles and shotguns were made and custom fitted for clients who wanted the quality of a hand made rifle pistol or shotgun But didnt want to spend fifty thousand dollars and wait three years as you would for a Boss.
A Bost shotgun can range in the range of $200 to $3000 depending on the condition of the gun and the detail of the design.
They are a tight gun well built and have the guild stamped of the craftsmen that built it on the barrels,frame or recievers.
Some will have the initials of the owner it was commisioned for.
Spainish Firearms are not the most desired firearms in the world but they make some nice ones. It depends on your taste.
Some people would never own a Reminton or a Belgium made firearm I hope this helped you out a little more.
Remember they are very rare here in the U.S