Hi,

As far as a MIDI connection to your computer is concerned you can use a USB to MIDI adapter. A quick search of the internet shows a number available in the UK. Pricing appears to be around 40 pounds. If your PC has a games port, a MIDI adapter for this should be available at a somewhat lower price.
As for the pitch bend wheel, if your GA3 accepts standard pitch bend control commands, most keyboards with a pitch wheel and MIDI output should work. It should be possible to pick up a quite cheap second hand one. Alternatively you could investigate inserting Pitch bend commands into a MIDI file on your PC.

Cheers
Len C.