I am searching for some small road wheelsets suitable for a heavy haul road trailer I am building.  The type of trailer used for hauling locos around by road. I have sourced truck wheels but the lowloader multi axle trailers have smaller wheels and I have not found a source yet.
   Can anyone help please ?

If all else fails you might be slicing some tubing.

http://www.ema-models.co.uk/index.php/plastruct-fineline-styrene/round-tube.html