Digikey and Mouser have a tremendous range of components available. But they do have very good filters on their webpages where you can narrow down the specs to select what you want. There are other vendors of electrical equipment and components where if you don't know the exact part their selection tools are virtually useless.
Mouser has been around for many decades but in their early days they focused mainly on connectors like those for coax, banana pins, clip leads, etc. They had a very small catalog or flyer you might call it.
When I was a kid I was able to convince my dad once in a while to take us to the main Allied store and distribution center at 100 N. Western in Chicago. It was amazing to see all the equipment on display. They had a will call where you could pick up parts. But when Tandy (which owned Radio Shack at the time) bought Allied they ruined it. They started adding a "handling charge" that seemed outrageous (something like $8). I went with a friend once that tried to convince the receptionist that we could "handle" it ourselves, and this seemed to confuse her for a while but then her boss came by and shooed us away.
Other good places to order were Burstein-Appleby, McGee, Fair Radio Sales (which still exists).
Locally we also had an Olson Electronics store.
