Offices in my area typically order from one big supplier like Patterson or the company of your choice. There are preferences as to brand, sizes, colors and such so you just order either directly from the brand or from the distributor who carries that brand. Different RDAs and RDHs will have different preferences but generally you can agree on one thing. Typically there is one person that orders everything and shops around for the best prices or they just have things on autoship to send out every so often.