Board Thread:Questions and Answers/@comment-70.189.158.65-20141121134044/@comment-1504072-20141121145008

I still believe that some weapons only appear in the shop at certain points in the game, but you should still be able to carry them over to the next playthrough once you've actually bought them. Some may also have additional requirements to unlock, but I cannot recall them offhand. If the requirements aren't listed in the weapons' respective articles I'd suggest checking out some online walkthroughs.