I should have mentioned www.catamaran.co.uk as well. It's not a commercial site - but it does have a decent For Sale page - with Prindle 16s, etc. I'll also be at Bala if you fancy a chat - Shadow 067.

You could try contacting 'local' sailing clubs too, such as Penmaenmawr, Llandudno and Llanfairfechan.