Sink manufacturers
generally design and build their products to fit in standard cabinet sizes. If
your cabinets are custom built, that may not be the case. Either way, sinks can
usually be placed in cabinets that may nominally seem too small.
The important thing to look at is the cross section of the sink or rough cutout
dimensions. You should be able to find this information on sink manufacturers’
websites. There will be a paper template in the box the sink comes in that the
contractor will use to layout and cut the hole.
A 30” wide cabinet will have an internal dimension of 29 – 28 ½" in most cases,
and that is why your contractor wants that size sink. The reality is that a 30"
sink will fit in the cabinet, but may require that the carpenter trim back the
sides of the base cabinet in some cases. My guess would be that the contractor
just wants to be sure that the cabinet will fit easily and the plumber can make
all the connections without too much trouble.
If the cabinet is on site or at least selected, you should be able to get the
exact interior dimensions. Work with the contractor to verify that the sink of
your choice can be made to fit, but I would be surprised if a 30” wide sink
could not be made to fit in a 30" wide base cabinet.
I don’t have any recommendations on where to look for sinks, but there should be
some ads that display on this page that might help. If you don’t find what you
are looking for, just Google plumbing fixtures and you will find many
possibilities.