robf, I'm modernizing a Turbo Optima that I've had since purchasing it new as a normal Optima in the mid-80's, and hopped it up to a T.O. a year or two later. Recently, I was trying to find aftermarket wheels on eBay by doing searches with "Optima" in the search, and was getting NOWHERE. What's important to realize is that all Optimas/Ultimas have 12mm hexagonal drive "washers" (except the fronts on an Ultima). Do a search for "kyosho 12mm" or something, and you'll find DOZENS of aftermarket wheels to choose from! And they're WAY cheaper than original repros!
Check out these 2 wheel sets I just purchased from an Aussie guy...very reasonable price, and shipping was under $23. 2 sets of 4 wheels & tires for under $60...the style options are endless! These ones have a slightly higher diameter than the Turbo Optima wheels & tires, but only by 5mm or so.
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=390199361414&ssPageName=STRK:MEWNX:IT
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=390217767587&ssPageName=STRK:MEWNX:IT
And here's a set I'll buy soon, too...these are gorgeous! Though the seller didn't include size specs or mounting specs, I messaged him and learned that they, too, are 12mm hex drives and similar in size to Turbo Optima wheels.
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&item=370408477134