What do you think of these?
http://www.schottwheels.com/wheel.cf...d=572&wid=3148
Don't be surprised if Swain chimes in with something Budnik has to offer or has the ability to produce. I see a few that look close but might not have a Cobra calibrated eye. Having said that, The right combo can really lend itself well to the look you might be seeking without being "correct".
Track Junky has a good suggestion and I would talk to Newstalgia wheel too. I know VWW introduced 18" sizes in the v40 and v45 a year or two ago. It is worth inquiring if their Shelby style wheel is coming in 18's but their site shows 17 as the max.