Have a look at this site, they don't list your tug but they are worth asking:
X List Model Plans
If you tell them it was originally a Model Makers Plan they might be able to put you in the right direction.
Have you seen this?:
mt FLYING DRAKE built by A & J Inglis Pointhouse Glasgow Clydebuilt Ships Database
or this, go to the bottom:
http://business.virgin.net/metcalf.m...sandmodels.htm
and here, you have to sign up to be able to see the pictures:
Flying Duck - Ships Nostalgia
There is also here:
Models By Design : Our Boats
There are obviously a couple of guys worth contacting here:
SFMBC.net :: View topic - Flying Duck
and I'm sure that Metcalf Mouldings will be able to help you out with plans and assistance if your model was originally one of theirs or a "Boats and Models" of Norwich, which it probably was!
Metcalf Mouldings Home Page
They do state thay they supply the original drawing for these models even though they have not decided to continue production of the kit.
I hope this is of some help.
Good luck and let us know how it goes.