With the number of poor quality tyres that are sold at the local tyre joint, combined with the fact that legally you just can't go anywhere near that speed, I find it difficult to fathom the logic that deems this requirement necessary for compliance or registration
FWIW - I believe my 15inch DOT rated Avons CR6ZZ are "V-rated" which is 240km/h from memory.
So there are probably other brands in that size also rated better than the 185km/h S or T ratings.
Best of luck with it