I suspect any custom and perhaps some semi-custom cabinet makers would make a vanity to those dimensions.

Try Omega Dynasty/Omega Custom, Bertch, Crown Point, Plain & Fancy, etc. Check the Finished Kitchens Blog from the Kitchens Forum for a list of cabinet manufacturers. See link below.

Click on the "FKB Categories" link on the right side to get to the Categories page.

Then, scroll down until you get to the "Cabinets" category. You'll see a list of cabinet manufacturers. Some are stock, some semi-custom, and some custom. It will at least give you a starting point.

HTH!

Here is a link that might be useful: Finished Kitchens Blog