[te51levin]

I think you're correct on the "official" part number, and you're right that we can't get it. But I have it on good authority (from mr220v) that Toyota oxygen sensors aren't really that specific. You do need a four-wire sensor, but apparently any four-wire Toyota sensor that plugs in will work. The wire colors may be different, but apparently they're always in the same order in the connector, so if it plugs in, it should work. Obviously it also has to fit the exhaust and have a reasonable wire length. If you're using a Toyota sensor, make sure the part number starts with 89465. If it starts with 89467, it'll be a wideband sensor, and that won't work with your ECU.

Assuming for the time being that a GenII sensor will work, here's the price on that:

89465-29365 - $125.41 - Oxygen sensor, GenII 3SGTE

I only have my phone to take pics with at work, so this is a little fuzzy, but I took a pic of the GenII sensor above so you can see roughly how it looks. Hopefully this helps at least a little.