for the type 99 rifle, it is semi rimmed correct...

www.natchezss.com may have some.

7.7 does appear to be semi-rimmed. I got tired of looking for ammo and got Norma brass and some bullets from Midway and reloaded my own. It is the same size bullet as the British .303

www.ows-ammunition.com/

40 bucks a box thu came up when I searched on there for 7.7 jap.
I suggest rolling your own.

You can convert 8x57 (8mm mauser) to 7.7 Jap. I did it and it works fine.
Look up the exact procedure online since my memory ain't that great but if I remember correctly all you have to do is neck the case down then fire form using very low power loads. I can't remember any trimming involved but please research this more before trying!
Oh, it is not semi-rimmed of course but it still works.
Editted to add;
I think Grafs might carry new production 7.7 Jap, I know they carry the brass and dies.
www.grafs.com

Editted one last time to add;
www.grafs.com/bulkByBagQty.cfm/startItem/1
19.99 for a box of 20

Thanks guys. I added a type 99 to my war colection, though I may never shoot it I would like to have some ammo for it...

tried your IM its full!
a local gunshop here has three boxes of loaded norma for 28.00 per box.
thats the cheepest around that I have seen.
he will take 75.00 for all three plus shipping.
Ill be happy to do the leg work if you need it.
Its been sitting on the shelf for at least five years I know of still bright and shiney.
(its next to the 6.5 carcano) amd other oddball stuff.)
hunter