Don,
Have you thought of having a look around the manufacturers websites for a model ship that has a dinghy on it and seeing if they will sell you one seperately?
I am doing a Mountfleet Ben Ain, unfortunately in 1/35th, but she has two ships boats as a fibreglass moulding that requires cladding with planking and adding the thwarts etc before adding them to the kit. If you can find something in 1/20th or 1/24th maybe you can get hold of something.
Have a look at this for example:
http://www.mountfleetmodels.co.uk/pi..._britannia.htm
I am sure if you give Mountfleet a ring they will sell you the fibreglass hull of the dingy that you could finish yourself.