RB30 Starter motor should
fit, as will one from a later RB20, i.e. R32. Tentatively I'd say any RB one will work...Best shot would be to go to an import wrecker with the offending item and compare and use the newest one which will fit.
Otherwise many auto electrical specialists can rebuild them.
It is a soul destroying trial to try and remove/refit the starter with the engine in the car, I am warning you now.
I believe you can adapt strut tops from the Aussie cars...Have not tried however. I would imagine the rubber is the same for both, get a urethane replacement aftermarket.
Rear wheel bearings, you have two choices. Knock out the old ones and go to a bearing shop, or just buy them new from Nissan (around $270 to kit both sides with bearings and seals).
Power steering pump is dual chamber and unique to HR31s. I threw mine out I am afraid
but there would be many places who can rebuild them.
Power window motor should be available new from Nissan ex-Japan in the short term.
Do check out http://www.r31skylineclub.com
I wish him good luck, these cars are brilliant when working correctly but can hide many costly and obscure problems.