I had the same problem with my alltrac. The 90 degree adapter that comes off the back of the transmission housing was rusted up and the short key shaft had the ears sheared off since the adapter wouldn't spin. After soaking the adapter in PB Blaster penetrating oil, I was able to free up the mechanism inside and get it to spin freely again. I was able to get the small shaft I needed for about $12 from the toyota stealership.
There is a write up on the MR2 speedometer setup that is the same as the one on the alltrac camry here:
http://stephenmason.com/cars/mr2speedo.html
This is his picture of the parts in question
A: 33403-19406 Gear sub-assembly, speedometer $29.67
B: 83798-17010 Key, speedometer adaptor $9.95
C: 33404-17010 Sleeve sub-assembly
D: 83770-17020 Adaptor assembly, speedometer $94.17
The part numbers should be the same for the alltrac Camry and the price for the Adapter assembly is $79.08 at:
http://www.toyotapart.com/
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90 Lexus ES250 Auto, 90 Lexus ES250 Stick, 88 Camry LE AllTrac Stick, 88 Camry Wagon

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