Hi, @damanton.

Your existing sink is most likely attached to the bottom with metal clips and silicone. Besides the fact you would need to find a new sink with the same 'cut-out' (shape) as your old sink, you need to first determine if the old sink can be removed. If your sink base has 'butt' doors, meaning no vertical piece of wood between the two doors, there is a chance. Perhaps the old sink could be unfastened and lowered into the bottom of the sink base (if your cabinet has butt doors). But then if the sink itself is wider than the width of the door opening (left to right), the old sink might not be able to be removed. If you have a typical 36" wide sink base, the overall opening door width would most likely be 33" (if it is a 1.5" face frame style cabinet). A lot of builder grade sinks are 31-32" wide. Then, your next concern would be finding someone who would install a new sink while the granite is still in place.

Look up posts by Joseph Corlett, LLC. A big part of his business is replacing old double sinks with new single sinks without removing the counters. He is out of the Tampa/sarasota FL area, but might be able to recommend someone in your area.