Google: plumbing supply {your town}. Call and ask if they sell to the public.
Don't bother walking in the door until you determine if they sell retail AND if they sell at reasonable prices. Many years ago, many (most?) supply houses, electrical, plumbing, HVAC, were good ole' boy's clubs that would either refuse to sell to the public, or offering to sell you stuff for list price and more. That trend died out hard, when everybody gained access to a Lowe's or HD that has 99% of what a typical DIYer will ever need. There are still two regional HVAC/plumbing suppliers in my area that are either ridiculous when it comes to pricing for DIyers, or total dicks to do business with, and have a belittling attitude toward anybody who isn't part of their steady customer clique. Hard to believe that a corporately controlled supply chain would be so poorly managed that top level management either doesn't know, or care, that their employees treat the walk-in trade like an irritation that needs to be ripped off.
This situation is, fortunately, very case specific. For example, I needed a large quantity of an odd sized electric cable that the local lowes was out of. I stopped by a random electrical supply house, in a city that I never do business in. I ended up with first class counter service and paid 40% less than Lowe's price.
