Due to the extreme age of this round, AND the VERY limited run of guns in that caliber, the odds of finding factory brass in that length probably rates comparable to my friend Aaron Goldberg being picked as Pope.
BELL has made a business out of selling brass that could be adapted to feed orphan guns- and I think that is going to be your route. Trail Boss has a good rep for low pressures, NOT being position sensitive, and may be a good choice. I know that the 40-65 and 45-70 have load data of a 400 or 405 gr bullet over 11-12 grains of Tail Boss, running about 890 and 970 fps respectively.
Article I ran across on the carbine ammo if you have not seen it- http://www.oldammo.com/january10.htm
You CAN check with OWS, but that will be a tough one. Good luck-