I got my hubcentric H&R wheel spacers from motorsportworld.co.uk, the had them for the best price I could find, and the best quality and fitment spacers, very light but very strong. They also sorted me out with extended wheel bolts to suit too as I needed 15mm spacers.
As for what size you need start by having a look on the wheel, see if it has the offset (et) stamped on them somewhere, or do a little research see if you can find out what they are, then you need to end up with about et32-35 when it's all fitted onto the car.
So for example my set up: wheels et50 - 15mm spacers = et35 on the car.
Either that or see what you have laying around and make yourself some replica spacers, something to put between the hub and wheel, I had some real thick cardboard packing boxes laying around which I hacked up and stuck on the car in layers till the wheel cleared just fine, then measured the thickness.
Hope this helps.