Are They allowed to do this? Discrimination? Trading Standards?

I think that the answer is yes they can. You cannot force someone to sell you anything. I very much doubt that it would come under the heading discrimination. The Trading Standards people are very unlikely to get involved. With expensive items like narrow Boats, Light Aircraft etc it is quite common to form a limited company as the management agent for the item. but really it is a formation of part owners being businesslike. It is not much like a normal trading company. You would probably save your self a lot of hle by looking to buy a small share in another boat.