Not sure what you mean by the “standard” trolley,  as there are several different ones.

The one with the rather nice twin cradle arrangement,  with padded vertical ends to the main cradle which give lateral support to the hull and can assist with docking, is essentially a West Mersea Trailers design,  although there are some clones of it around.

Try West Mersea Trailers,  or Mersea Trailers (NOT the same firm  –  very confusing),   http://freespace.virgin.net/trailer.sales/,    http://www.merseatrailers.com/home.php;   or Chris Brown, http://www.cbcoverstore.co.uk/.

A launching trolley with a more basic arrangement of chocks is (or at least was) made by Rapide,  as part of a combi-unit;  and I am fairly sure that Indespension also do one.

Yet another design of combi-trailer is produced by Sovereign Trailers.    I had not previously heard of them,  but there was an article from them about the new trailer legislation in the Spring 2013 issue of Mainsail.

I rather doubt whether launching trolleys of differing designs are interchangeable with road bases for alternative designs,  so it would be sensible to first identify exactly what launching trolley you have.     However I have successfully used a launching trolley from Chris Brown on my West Mersea road base,  but then this launching trolley is a near clone of the West Mersea one.

Hope this helps,  and good luck.

Oliver