If you can get down to SE CT we can load up all that you want...and shoot some onsite to boot.
Needless to say, bring your rifle!
Contact me for component availability, since I'm running quite low on most items.
I'm here just about every day...
Years ago, Hoffman's in central CT, had three bags of virgin 7.7x58mm Prvi brass collecting dust. I'm sure they are long gone by now.
Also, Hansen's in Southport, CT
had crates of 7.7 machine gun ammo on strippers. This is a semi-rimmed cartridge, not for the Type 99, but it's the only "official" 7.7 Japanese military issue I've seen.
There is a shop in Branford, CT that has the most diverse collection of mil-surps that I've seen in state, but he doesn't do walk-in retail (??...mostly auction web-site activity apparently). Had a wall full of Arisakas, a few years back. Can't say what he has for accessories nor real-world prices.
http://fflgundealers.net/hunters-shop-the.html