Mike Signs
808 Greenwood St, Evanston, IL 60201
(847) 869-9390
Ask for Maria, or Chris and tell them that Ty from Team H4R sent you.
I don't know how their prices will compare for a company that already makes specialized SCCA type magnetic decals, but they did a good job and for a decent price on the magnetic decals my team uses.
Only other possible catch is that they prefer customized business, don't expect them to have pre-made magnetic decals. If you're good at Photoshop or even better at Illustrator and can export vector-based graphics all the better... the decal cutter cuts based on vector-based files
Otherwise you can bring in a printed or photographed image that you want them to emulate (they're really good at that).
lateRZ
[edit: Just FYI, Team H4R is sponsored by Mike Signs, so our pricing is not necessarily what you will get. Garage Kwai and FIRST GEAR are also clients of Mike Signs]