I'm curious. Where to people that build computers for a living get the computer parts?

Do they buy them from the same places other people do like tigerdirect or newegg? Or do they have a special supplier?

shop around for the best prises .I am not vat registered and like to slip under the radar as it were lol .To buy wholesale you need to buy a lot of hardware and holding onto stock is not a good idea with prices as volatile as they are

They probably use many resources... unless they are building big quantities-- in which case they'd probably put out contracts with specifications for suppliers to bid on.

Most register a business name so the get a business number for trading with wholesales to get a wholesale price then NewEgg and other suplier can give you a wholesale price list.

I buy all my parts wholesale - which in Australia requires that you run a PC business of some sort and have an ABN.
To get accounts with wholesalers in general you need to be spending more than $5,000-$10,000 per month but they will still supply you as long as you pay upfront.