Its best to have a look at specialist auction houses such as www.vectis.co.uk who hold auctions at Rugby every 2 months and who archive auction results for reference. They do have TT going through from time to time. You can always set a reserve against any valuations they make for your collection.
They do take 20% commision (incl VAT) though from sellers.
It is a specialised area and I'm not too sure that there are actually any dedicated Triang TT dealers. I'm not convinced that normal stockists who buy in secondhand kit would make a sensible offer.
Miles Rowland at the Tri-ang Society may also be able to help.
Happy modelling
Gary
They do take 20% commision (incl VAT) though from sellers.

It is a specialised area and I'm not too sure that there are actually any dedicated Triang TT dealers. I'm not convinced that normal stockists who buy in secondhand kit would make a sensible offer.
Miles Rowland at the Tri-ang Society may also be able to help.
Happy modelling
Gary