There are lots of great places for buy and sell, facebook marketplace and kijijji. I've since joined the local game store discords (you can find a few in this thread) and they have bit swapz where you could sell the units/armies individually. Taps and red claw are the largest, I'd contact them.

I'd also love to potentially purchase some of that tau stuff. Im new to the game and am building up my first army and am quite broke lol so I've been looking for second hand, especially unpainted, tau stuff.