If its an odd size, then you may have to get it made. If not look for cabinets that are 33-34 tall, 20-22 inch depth (finish dimensions). Kitchen cabinets are a bit too tall(sorry Noah) unless you are 6'5"
I have installed a couple of their cabinets before where clients have bought from them. They seem to be in ok quality.
https://www.builderssurplus.net/products/bathrooms/?msclkid=2c01a8c59f81135f869cf3a91e23ec03&utm_source=bing&utm_medium=cpc&utm_campaign=Vanities&utm_term=Bathroom%20Vanities&utm_content=Vanities