I agree that a large single sink is a better way to go.
I would search RV sites and talk to RV parts places or manufactures... they have a large selection of sizes and styles to choose from, but it may have to be ordered..
a new counter top may be necessary depending on what you have, but I have seen where the existing hole was filled with a cutout "plug", and then a new laminate layed over it all, with the new hole cut where desired and sized according to the new sink....
some think a double sink is necessary or convenient for washing dishes, but it definitely is NOT in a small space....
we have a single sink on our 34, and for washing dishes we use a spray bottle with soapy water in it... any dish that gets placed in the sink gets sprayed with the soapy water... it starts doing its thing.
the dishes may set in the sink most the day before we get around to washing them, but when we do its only a matter of spraying them all again with the soapy water to wet them up, and then scrubbing to loosen any hard bits of residual... after they are all scrubbed and laying in the sink, then they get a warm water rinse.... (with the dishes being cold, the soapy water doesnt dry on them while they are waiting for the rinse, and the pre-spray when the dish was placed in the sink starts breaking down the proteins so stuff like egg yolk doesnt dry out and stick to the plate as hard if it should set for hours before getting washed).
this method saves water and time..... the same method can be performed with a double sink, but its better to have more room to work in than less, and without the sink divider, there is a lot more room..... I can see no practical reason for a double sink in a small space.
we keep a couple of tubs on board for various uses, and we can use these when we have guests and want to place the dishes in the tubs and out of the way until we have the time or counter space to wash them...or wash them in the cockpit.
Ive had boats with double sinks and much prefer the larger, single basin style...