The nice thing about Stevens 44 & 44 1/2 rifles is that the barrels are interchangable. They are simple to remove, The extractor is very simple to replace. You could get a 25-20 barrel & extractor and shoot your gem.
I believe your rifle is a model 47 and has a very nice Stevens 103 tang sight.
Your best source for brass is RMC as Vall mentioned. I suggest that you do a chamber cast and send that to RMC,
I have not seen any 22-15 brass for sale for many years. I almost bought a Stevens 44 in 22-15 from James Grant but could not find any brass.
