Once upon a time, we built Heathkits and Knightkits and got our resistors, capacitors and solder from places like Allied, Radio Shack and Lafayette Radio Electronics. Allied has had a renaissance as a mail order parts retailer, but brick and mortar stores are fading into the sunset.
Elecraft remains the premiere purveyor of build-it-yourself ham gear, making much of its high quality equipment available fully assembled or in kit mode.
For Allied fans, here is a link to an archive of their famous catalogs.