I've managed to scrounge up forty rounds for my Arisaka over the years but most places now don't carry them anymore.
"Gad Custom Cartridges" claims to have 7.7 Jap.
I have no idea if they are good to deal with or not.
http://www.gadcustomcartridges.com/
Mike

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"I think myself that we have more machinery of government than is necessary, too many parasites living on the labor of the industrious."
Thomas Jefferson- Letter to William Ludlow, September 6, 1824