http://www.mstyle.co.uk/acatalog/BMW_Z_Z4_Z4M_genuine_BMW_wheels.html
They will add tyres at competitive prices too, and delivery was cheap or free iirc. They will offer new bolts/caps too at BMW prices iirc...
I spent £40 fuel travelling and a full day to go pick up 4x Ellipsoids with old RFT Bridgestones for £200, then another £260 getting them reconditioned (included new tyre fitting), but I had to order/deliver tyres and then go take wheels to recon place too.
All in, about £500 in time/hassle, and the recon is 'good enough' but think £350 to get them done in wet paint, so another £100)
£200-300 extra to get them brand spanking new with no worries about dinks or bad kerbing etc, and fresh to fit new tyres of your choice... kinda wish I'd gone that route now.
So, unless you can find MINT ones (and I mean perfect original), for about £450-500, then I'd just buy brand new. In the long run it'll save lots of hassle. Just make sure you don't kerb them!
Dave