I have no idea how to find the right trailer for my boat!
You need to figure out if you just want to do a one time transport or whether you want to be able to trailer your boat (launch it or transport it regularly). If the former, you''d probably be better off paying a boat transport outfit to convey it.
Used boat trailers in good condition are harder to find than the holy grail. Most of the ones on the market tend to be ones that have not been well cared for and need substantial work (brakes, frame rust, etc.) Check ebay, check iboats.com, check the internet. You will probably have to modify whatever you locate. Depending on how heavy your boat is you may need dual axle. In this weight range almost every state requires brakes on at least one axle to register the trailer. The most commonly available used trailers are powerboat trailers, but your keel is probably too long to work on a roller trailer. Proabably you''ll need bunks on risers (raised enough for the keel to clear the axles). If you want to launch on a ramp from the trailer you might want some sort of keel rollers on the cross beams of the trailer frame.
It would also help if you could find a website/list for Kells owners and post a query there.