Real estate agents/investors don't (Shouldn't) have access because they won't pass the "Permissible Use" requirements.Yes...people every day use Accurint and other similar data suppliers.

Walmart knows more about the costs that go into a product than the actual manufacturer and will squeeze out as much profit from the supplier as they can to get the costs down.

That said, I've gotten and given referrals for my rock-star contractors, I want them to stay in business, and to remember me when I call them for help, so just asking other landlords and rehabbers for referrals works pretty well, as does asking for help in finding sources for materials for the same reason - the niche suppliers like the molding store I buy from don't make much money off me, and they're about a third the cost of the depot, so I pass their numbers out at every opportunity to keep them alive.

Check locally tooI was able to get my blank signs cheapest from a local bulk sign/plastics supplier 

There are a couple of online suppliers that are willing to ship, however the countertops being done that way are made in china and of terrible quality.

Builders First is a national supplier of building materials. 

During the pandemic, out $5 curtain supplier ran out, and my wife ended up resorting to having to sew the sheers herself for one property.

Reality is, when supply outpaces demand, the suppliers are in competition for the limited demand. 

Lucky to have connections through work to get cheap materials from our suppliers.  

If the builder doesn't finish the construction, your property can be liened by subs and suppliers.