Try all the second hand shops - my mate has a shop on King Street Wallasey and he is often offered stolen stuff but will only deal with folk who have current ID .... that sort of bike is going to be hard to get rid of to 'normal' bike riders though ...you need to put the word around Trial bikers and their associates and fer reaching websites
are these trials bikes common? I have never heard of them before but when I read this post just then I remembered that I had just seen one for sale on 'fleabay' on facebook. Will send mistybluered a PM with the link