Well, obtainable varies country by country.
In the US, almost anything is obtainable, either as new, or from surplus shops.
For example, I got some nice 20 button calculator keypads from Surplus Sales of Nebraska, had not seen anything that else where, just standard 12/16 button velleman keypads.
www.mpja.com has lots of nice surplus stuff, got really bright (3,000mcd, 5,000mcd, 10,000mcd!) LEDs for like 18cents each, shipped next day, no waiting for shipment from China. Also 90dB 2" speakers for $1.49!
If you're just breadboarding stuff, the list of needed stuff is different than if you're actually assembling something, in which case a hoard of #4 nuts, bolts, plastic spacers/standoffs, headers and things to plug into them all come in handy. I stocked up on pololu crimp connector housings and terminated male-male, female-female, and male-female wires so I could have some options for assembling projects.