Yeah, see how the car runs with the battery disconnected, if it really struggles it could be your alternator.
Check for a voltage across earth wires and the battery to alternator wire (it should be low, otherwise there is too much resistance in the conection)
I'd hazard a guess and say you could use most toyota internally regulated alternators? (ie visit a wrecker)
I've had a very similar problem with my 4ac, it turned out to be a bad earth...
