The only way to get Typhoons sold to Japan would be to get Japanese manufacturers (starting with Mitsubishi) into the EADS group's stock with a significant %. Daimler is getting out, which leaves space for new entrants.
Japanese manufacturers could build parts of the jet and of plenty of other civilian birds (A350 for instance). A sort of Euro-Japanese alliance.
I'd still bet more on F35s though
Btw, Japan should change its spec : by now they do need fighterbombers, not pure air defence fighters ! The JSDF are evolving fast into full blown armed forces and Parliament has even reinstated a Minister of Defence (previously JSDF was an Agency, below ministerial status). Shouldn't be hard to justify procurement of a real fighterbomber with cruise missiles.
cheers