All the above are correct however there is on other issue you may need to address. If your product is similar to others on the market then you may find that the larger supply stores (wholesalers) that are nationally run have what we call trading agreements with existing suppliers and unless your product has significant advantages they may not be prepared to allow you to sell your products through their stores.
In this case the best idea is to create the demand to force their hand. Again though you product needs to have advantages (features/price etc) as plumbers can tend to be very loyal to products they know work. You only have to monitor the postings here to see that.
Follow the advise of the others with regard to direct mail and advertising and trade shows but be prepared for a lot of work.
