[HeyLaughingBoy]

For small to mid-level production (singles to mid-thousands per build), most shops will use a distributor like Digi-Key, Mouser or Arrow to source parts. Above that, you can start talking to manufacturers directly in some cases if you can't get good enough prices through distribution.

What throws this off is that a lot of shops these days use Contract Manufacturers (CM's). Since CMs are building boards for many different shops, they can purchase parts in larger volumes and get better pricing. They make it easier to outsource some of your manufacturing since you can just give them a BOM (Bill of Materials) and your PCB files and get complete, tested boards back. So you don't even need to deal with parts shopping, etc.

As far as inventory management, if you're not big enough to be using an ERP (Enterprise Resource Planning) system, it's likely a Quickbooks plug-in, a spreadsheet or something custom built.

IME, as long as they people can meet their BOM price target, they just buy from whoever they're used to dealing with.

I have a couple products in low-volume production manufactured in my basement. 90% of my components are purchased from Digi-Key because we're both in Minnesota (and Digi-Key is the best vendor I've ever dealt with) so most things I order arrive the next day without having to pay extra. They also have BOM tools on their site: I can create a bill of materials for a board to make it easier to order parts: just bring up the BOM and enter a number of units and it will create a shopping cart for me.

I'll occasionally look around for better prices on some high-cost parts, but it's hardly worth it at my low volumes: there really isn't enough price variation on most things.