Once upon a time, electronics enthusiasts could go into their local radio shack, and come out with most of what they needed to homebrew radios, antennas and other cool stuff.
But now, most of those items are only sold online, dominated by Amazon, and Ebay in the search results.
If you aren’t finding what you need in those places (or don’t like the rising prices born of monopoly of search results) here are some of my favorite sources.
Components and tools for radio, electronics and Arduino, Raspberry Pi, Power supplies, DC motors, Cables & Connectors. Best part: prices are pretty reasonable. ~$7 flat-rate shipping, so very tiny orders are not recommended.
Electrical components, kits, batteries, power supplies, cables, breadboards, robotics parts, testing tools, ICs and Semiconductors. Nice selection and reasonable prices. Very small orders not recommended due to small order handling charges.