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Look up the CTC (cyclist touring club). or to a lesser extent Audax UK. 

That is your market and you may well get some feedback from CTC if you email them 

Edit:

Also you could try the cyclechat forums. It is quite a large forum but a little friendlier than the main one Bike Radar.

Have you thought about approaching local bike shops, also pannier manufacturers may be an idea ortlieb?

Good luck