I don't know if this will help you or not, especially me being in the states--the somewhat united ones .
Last time I needed a belt for an old bandsaw, I ended up, on the advice of another, going to an auto parts supplier and they matched it pretty good. It was a tad long for which I had enough adjustment so it worked out ok.
Don't know how far you are from Hereford but the following firm keep a massive supply of belts of all sizes in stock. If they don't have what you want, they will make it up for you, and they don't tend to be expensive.
CBS Rotary Power Motion Ltd.,
Unit 14, Grandstand Business Centre,
Might be worth a 'phone call if you can give them the size you need. I don't know whether they do mail order.