I've seen previous posts on a group buy for a specific spec rota wheel, although I don't believe they got the ball rolling on that one. Rota is probably the last on my mind for wheels. Don't get me wrong, they are great for the price.
If that deal does go through I may have to jump on that special made set if I can't find anything before then.
Diamond might make something in that size, but it'd be likely heavier than you're looking for. Any weight goals you have?
14x7.5 is, at least for Miatae, not a common street car size, probably because 14's are becoming more rare in the first place. I'd bet that there are not many street tires that would fit on it (properly).