What I would do is find out if they are making a good profit or being over charged, if being over charged make them a better offer.
If they're making a profit, suggest to them to lower their prices.
At the end of the day you're going to make more money if you have them on board being the offical supplier sounds much better and would be better for the club.
Also think about getting adverts in the programmes, if latics fans know about what you can offer they're more likely to buy your stuff.
Get yourself a website if you're planning on making into a business, if you need help with that side of things message me as I'm possibly going to kick start off my own web development company.
Anoother thing you could look into not sure if they have them in oldham or rochdale, but have them in Manchester and Leeds stall in shopping centres that sell canvas prints or do them within 1 hour for you to pick up.