To offer a third pair of eyes, I think what yaris was getting at (and honestly what I thought when I first read the title) was you were looking for a supplier to print a custom sub-dye file for you, however by your post it looks like you are hunting for recommendations if anyone else has hired a designer to
make the custom sub-dye files.
If it is the latter, perhaps change the title to "recommendations for custom sub-dye file designers?". Might be better at getting the attention of those on here who may have previous hired someone or know of someone who can help you.
Unfortunately I cannot help you with the recommendation, but hope my 2 cents aren't out of place