I got some bits from euro auto salvage and some privately. I have to do everything with the legacy, clutch, flywheel, starter, gearbox, prop, rear diff, front and rear driveshafts, rear hubs, front and rear brakes.
You on the other hand need a 3.9 ratio gearbox to match your rear diff (and then the clutch, starter and flywheel as you plan on doing already). You will also need an automatic impreza prop shaft or you can have you own cut and balanced to suit. I'm not sure what front driveshafts are on yours, but you may need 6 speed ones to suit the box (or your own can be made to fit if you buy an adapter(not sure where you get it but someone else might know))