You can go to a big box store and order a vanity cabinet from a number of semi-custom cabinet manufacture's catalogs. They have standard vanities, but they also have vanity components just like individual base kitchen cabinets in their lineups, and then you can have it ordered in a "reduced depth" for an upcharge. If you want 36" height, you could even use kitchen base cabinets ordered at reduced depth. There may be a minimum depth for drawers in the base however.
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