I don't have a whole lot of great info on Colvic models. Try this link: http://www.yachtbrochures.co.uk/
. He has something on your boat. You'll need to Email him to find out if what he has contains the detail you require. It won't cost that much anyway, especially if you're in the UK.
He's nice guy. I have dealt with him a number of times.
Besides what Barney suggests, see if there are some others around on the hard.
I don't know how many of these were made.
Let me know how you make out.