Wanted! A small piece of sail for repairs

Originally posted by Rupert

   Last year myself and a friend acquired an unloved Freshman dinghy that required a lot of TLC to get it back on the water. We've spent many hours restoring it to a usable state, and are almost ready to start sailing it (or at least try).
The last job is a repair of the mainsail. This has a couple of smallish holes (approx 5cm x 8cm) where something has eaten through the cloth.  The rest of the sail is nothing special, quite with a few stains and other small holes.

I just need a small piece of white sail to repair it, but am struggling to find some suitable material.  I have contacted a couple of sailmakers hoping to get some small offcuts, but is seems they are only interested in taking the sail from me and doing the full repair (fair enough - that is their business). But we are on a very tight budget and are trying to do everything ourselves.

I have asked the local sailing clubs if they have any discarded sails that are not fit for use, but no joy.  Ebay only seems to have complete sails for sale, and these got for a minimum of £15+, and it would be a real shame to destroy a perfectly good sail for the sake of a square metre of cloth to repair our Freshman.

Does anyone have any ideas how I can proceed?  I'm based in the Thames Valley.

We will be travelling to the Southampton Boat Show, and I'm planning to harangue and hassle any sailmakers I find there, but otherwise I'm not sure what to do.