Yes there is a supplemental manual for the '94 you can purchase but I don't know of any free online versions.
The '92 and '93 model years are basically the same, not exactly but close enough. The '94 model did however have some noticable (or maybe not-so-noticable) differences.
Some of the minor differences for the '94 year included standard driver and passenger-side airbags as opposed to just the driver side (GS model), the rear seat room increased by 1/2" (very minor but true), the gas mileage changed slightly, the steering rack was re-engineered to help isolate the driver from road imperfections (this was in response to the Lexus ES's smoother handling), and the suspension was softened (also in response to the ES).
There are a few more differences but those are just the ones I remember off the top of my head.