There are several places you could try to obtain a set of plans. The following may be of help.
Try the shipyard if they are still opperating, The Smithsonian Institution or The National Maritime Museum at Greenwich. If the NMM be prepared to take out a second mortage because they sure know how to charge. Failing that you could try one of the ship modelling companies that advertise in FSM. Also check in other ship modelling mags for companies that sell plans. You could check and see if there is an "Old Boys" Association for the ship or its class.
I hope that this is of some help.
Dai