were can i buy the 3 compartment sink and how much

you can buy that kind of sink from just about any commercial kitchen equipment retailer. Just google "3 tub scullery sink" and a ton of vendors will show up. I think they run about 1200 bucks or so new(just the sink itself - price can vary a lot pending gauge of steel and vendor) not including the plumbing and installation. You can get used ones also, as restaurants are constantly going in and out of business.

as a heads up, make sure the side wings are wide and tall enough to accommodate a residential dishwasher below - it will look bad, but be functional. Storage space is lost underneath also - unless you don't mind all that stuff showing or figure a clever way to install siding / cabinet doors over the sides and front...