Why not contact your local weld shop or metal fabrication shop. I am quite sure the trailer mfg is not going to be cheap. The easiest method was a sleeve method where you cut off a length of you trailer tongue and then have made a sleeve that fits inside the hollow tongue and remaining trailer tongue. Slip it together when needed and remove when in storage. If the fit is snug then hitch pins could be used, other wise a couple 1/2" or 5/8" bolts is all that would be needed. Any decent fab shop should have no difficulty in making you a sleeve.