http://www.maximummotorsports.com/MM-Wheel-Spacers-C231.aspx
I was considering getting some for my car, and these would be the guys I'd go to if I did.
Not being hub-centric means that you'll want to be fussier even about snugging the lug nuts down to 'seat' the wheel in place before torquing them. Even this initial step needs to be done to reasonably even amounts. Do not let the full corner weight rest on the wheel until you've finished torquing all five studs. Going around the pattern one extra cycle doesn't hurt, either.
Been there, with wheels that do not perfectly hub-center themselves even without spacers.
Norm
Check these guys out:
http://www.motorsport-tech.com/wheel_spacers.html
They custom make to order what you need, CNC in USA.
I ordered a conversion wheel spacer a while back when I wanted to fit some BMW wheels to my 350z (LOL the BBS wheels I wanted only came in 5x120) and I was able to order 2 different size for the front & rear sets that were hub centric to the car and hub centric to the wheel hub as well.
Great quality and pretty fast turn around for custom goods.
o2sys gave them a call and had them start on a set of hubcentric 1/2 spacers. Thanks for the heads up on that, i really wanted a snug fit on the wheel.
Great! Post pics!

Just FYI, I am running OEM Saleen 20x10s 35mm offset with 285s on the front with no issues what so ever.
What brand wheels were these and how did you end up making them fit over the Brembos?
The wheels i have a downforce df5 20x10 40mm offest. I used a 7/16 spacer.