On Toyota's counterbalance trucks the model and serial no is normally stamped on the right side of the chassis. Where the bonnet rests on the chassis of the truck. You might have to scrap of some paint to see it.

The model and serial number of a Toyota forklift can be found on the frame, usually on the right side on top or below the front protector.
The serial number is also typically stamped on the forklift, so it can still be identified if the data plate is missing.
Nameplate
Usually located on the dashboard, the nameplate may also include the forklift's weight, lift capacity, and mast information.
Frame
The model and serial number may be located on the front of the frame or elsewhere on the frame.

I can't find the serial number. I have looked everywhere. It is really old forklift. Any suggestions?

Unless you are real familiar with forklift trucks you will need the model and serier number to find the year.and model.