Very hard to find at gunshows, and there are a few variations, expensive and lots of duds, I am converting my current .25 rimfire to central fire, but this is expensive and many would not bother.
There was a .25 Short, .25 Stevens short, and a .25 Stevens, all are r.f. and all are long obsolete. The .27 cal. nail charges don't fit the Stevens chamber, but prolly would fit the .25 short, not sure about .28 or larger. I DO NOT RECOMMEND using these charges, I have played around with removing the charges and replacing with black powder and lead bullet, but should only be done by those that know what they are about.....Ben