One way to shop is to type in a rough description of what you want and used Google Shopping. Finding a sites and a more definite description I insert this back into the search. Then tweak and compare what you get by changing the ordering from price to rating. Searching the store site for a location and phone number can be handy. Inserting their name and 'complaints' or similar term can get you a reasonable estimate of their reliability. I follow up with an e-mail or a phone call to get some impression of how they handle customers and orders.

I find the best buying experience comes often from mid-sized online retailers. Often they are just a bit more expensive than the cheapest supplier but they often give it back to you in service.

It is often good to search for local 'medical suppliers'. Key there, as usual, is to find a supplier far enough up the food chain to get good prices but far enough down to be responsive to the smaller orders your likely to buy.

Collectivizing supply orders can get you big discounts. You get a much better price for 4by4s if you order them by the thousand. Coordinating with CERT, local volunteer FD, other prepers, and anyone else you can being on board, can save a lot of money.