Look around for "Hamfests".
Things aren't free,but if you are looking for odd bits you will be able to pick them up cheaply.
At one time,various companies which use Electronics would give away obsolete stuff to Electronics enthusiasts,as it cost more to dump them or sell them.
The "Health & Safety" freaks have pretty much put paid to that,though!
Sometimes you can find stuff at ordinary swapmeets,but,again,not as much as in earlier times,as people are wary of being sued if some halfwit buys Electrical equipment & blows himself up!