Either granite or quartz slabs come long enought but of course with huge waste unless you plan to do more things with the counter material and of course always the issue of moving that size around to go into the bathroom in one piece . You go to stone yard and choose a slab you do not go shopping for a "counter top" I agree we need pics.

It's a custom cut and polish for a new top, with under mounted sinks.

Go to a stone yard look through the remnants for half slabs.

Where is a picture, of what you are doing, as it should look good with flooring an vanity and any wall tiles as well.

Post pictures of the entire bath, a couple of angles as jpegs in a comment box below mine !

Yes, you will not find one premade at Home Depot. They could probably order one for you though with formica or some other product.

add photos of the dilemma, have you considered separating the sinks for a different look?

two vanities side by side with a space between?