If he was in Okinawa it was probably a type 99 Arisaka, which fires the 7.7x58mm (7.7 Jap.) While not exactly common you can get new production ammo for them online or ordered through your LGS for between $1.50 and $2.00 a round. Hell if it was the old Type 38 (6.5 Arisaka) its even cheaper. Not that amazing honestly.