Check this blog post which I wrote a few years ago about general places to buy electronic components, tools, supplies.
The list below documents where each component in the toolbox was purchased from. Note that many of them are purchased from Aliexpress.com, which is inexpensive but can take several weeks to deliver.
Note that some items below are bulk quantity (which makes sense when we purchase for the whole class). If you just need one or two, you can search in the same store for single quantity item.