[CharlesStevenson]

As regards other places

eBay
Autotrader
Friday Ads
Gumtree
Parkers

could be a good start (but I'm sure you knew that already)

but beware of over-priced cars, since, depending upon what your plans are, buying one that's standard but in need of some mechanical general service work could be better than paying top dollar for something that's had all that already done.