They are all over ebay UK. Trailer rules with US dot are the same as trucks-to be dot exempt on entry the trailer needs to be 25yrs old. That said, Customs don't seem to care on entry. I have brought in a Sankey and a replacement tub in containers. I would be happy to help others get one over within reason. Ie most of my containers load in Essex so look for something that's geographically desireable to there and then email me.
Regards,
Doug