Well, you certainly can get custom transformers designed and prototyped. I know that Marque Magnetics will do it, but they are in New Zealand and could be a little expensive when you consider shipping. They can do a full design and propose bobbins, cores etc. to suit. They also can give you a report on the construction and do a HiPot test on every part, which is reassuring.
I’m sure you can find someone closer, but Marque can be a backup for you.