is it possible to get an adapter plate so i could fit a set of rims onto my ba xr8 even though the wheels are off a vr statesman??

Any adapter fitted to the existing wheel studs would likely and probably necessarily be at least as thick as falcon steel rim wheel nuts. Can the car and rims handle an extra say 25mm of track? I guess not.

Do the rims look holden? If so you'll upset people on both sides, and it will be hard to sell!

As said above, unlikely. Minimum hub adapter width I was told was 25mm, any less and there isn't enough meat to hold the studs safely in, etc. So you'd need to be fitting wheels with an offset 25mm further than the BA ones - perhaps a set of Subaru wheels?

If your car was pre-AU it could be done. I've seen adapters for both Holden Commodore and Subaru wheels for Pre-AU Falcons on eBay.