I've bought and sold a couple, just about to buy another one actually
www.dvla-som.co.uk
www.pl4tes.co.uk forum
www.boldreg.com
The top three are realistic prices
These below are overpriced but you can negotiate:
ebay ...derrr
www.newreg.com
www.regtransfers.co.uk
www.nationalnumbers.co.uk
can we get Tom C 'T33 BAG' ??