I know it's the wrong side of Lonon for you, buy Moss and Co in Hammersmith sell a wide range of veneered boards. They also do veneered MDF, much nicer to work with than veneered chipboard, but very dusty so a bit of care needed.
Moss and co don't have a website AFAIK, their number is 0208 748 8251
There is a company called Panel Supplies, in Basildon Essex. I have a copy of their buyers guide. They do ply, mdf and chip board with veneered faces.
Their phone number is 01268 729100. Their web site is just one page.
I have never bought anything from them, but the stuff in the booklet looks good.