My type 99 Arisaka is extremely accurate. Crappy trigger, but when locked in prone and letting the trigger break as best as I can, I can hit the X ring every time at 100 yards. Hornady does make ammo for this rifle. Brass is also widely available.
I've had very good luck reforming 270 winchester brass to 7.7x58 Arisaka. I load 180 grain remington core-loks over 37-40 grains of H-4895. I'm not sure if any bullet manufacturer makes a long 174 grain military bullet similar to the original loading to achieve the proper OAL. I'm sure seating the rounds longer would help with accuracy as it appears the rifles have long throats designed for the longer bullets (this is also especially true with the 6.5 arisaka). Reducing the "jump" probably would increase accuracy, but in any case, I've attain very impressive groups with standard 180 grain .311"-.312" bullets loaded in the 270 reformed cases. The 270win case necks are not as thick so they do not have as much neck tension, but do not pose nay problem when going with a light taper crimp, or if you prefer, you can crimp at the canulure.