They would have C&R status, being over 50 years old.
Prices vary and there is no source of Type 99's (or Type 38 in 6.5 either) in quantity, as neither has ever appeared on the surplus market.
Many thousands of both models were brought back by GI's and they turn up from time to time in gun shops and at gun shows. Prices on the Type 99 range from $100 or so for a butchered one (all too common) to $300+ for an original one in good shape.
7.7 cases can be made from .30-'06 cases, but the base diameter is a bit too small. This usually gives no problem, but repeated full length resizing will weaken the case, so neck sizing only is the best practice. Recoil of the 7.7 is no greater than that of the .30-'06 and quite a bit less than that of the 7.9mm Mauser with 196 grain bullet.
While the Type 99 design is very strong, quality deteriorated during the war, and very late ones with crude bolts, fixed peep rear sights and wooden butt plates should be avoided except for collecting.
WARNING: There are Japanese training rifles seen from time to time that are meant only for firing blanks. AFAIK, all use the 6.5 blank and 7.7 ammo won't fit, but avoid any rifles with tiny or no locking lugs, a single piece cast receiver tang, and a smooth bore (again except for collection).
Jim