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mach1.3
The correct caliber for a Broomhandle (AKA: C-96 Mauser) pistol is .30 Mauser, or 7.63x25 Mauser. And yes, it's still available. The 30 Mauser was the "inspiration" for the Russian Tokarev 7.62x25 cartridge. Some WWI Broomhandle Mausers were rechambered for 9mm and the grips had a big red "9" on them for identification.
Here's some 30 Mauser ammo currently available (although there's probably not much call for it nowadays, even presently with all the idiotic gun & ammo buying feeding-frenzy going on):
http://www.cheaperthandirt.com/product/3-0315760
I didn't do any serious searching, but you can probably find more ammo available elsewhere.
IIRC, you can safely shoot 30 Mauser (7.63x25mm) in a TT-33 Tokarev (7.65x25mm), but not vice-versa.
Someone correct me if I'm wrong...