After you get to Japan, start counting all the gen4 Camrys you'll see. You'd be hard pressed to find 10 sedans during your entire trip, you'll see more Camry Gracia Wagons, but they were very slow sellers.
Anyway, the place to get stuff? There's usually an Autobacs (big autoparts store) in most cities. They hae a lots of stuff, but prices are higher in Japan for most things.
http://www.autobacs.com/world/
1MZ engines are used in many JDM Toyotas, but not on gen4 Camrys. Instead, a 2.5L 2MZ-FE was used.