The tyre fitter I went to gave me 8 tyres, fitted, and took 2 old tyres off me for a fiver and a drink. lol
They said they'd take any old tyres off me if I want, since they're employees and it's no skin off their back. Top stuff.
Otherwise they just sit in my back garden until I can find some way of disposing of them, usually involves pikeyness and hanging on to them for a while.