Did you buy them directly or through your roofer? If you bought them from the retailer the retailer should be sorting it out and then they should claim from the supplier. If the roofer bought them, you should claim against the roofer, who then should go to the retailer, who in turn should claim from the supplier. There is often a resistance in the supply chain to take responsibility so you may need to push.
Good, if it's info you want I would try either construction forums or roofing forums. Google the product name and problem/defective/issues. You could also search some of the construction magazine websites but this will be more of a fishing exercise. Tbh the best people to find out information are people in the industry talking to other people - so the retailer or your roofer are probably better placed to chat to other people in the industry than as a lay person. I get most gossip like that at work dos/events/cpd/lunches/drinks
Daisy, unless you're at a loose end with nothing better to do, leave the research to the retailer, and save your time and energy for making sure THEY put right the problem. Your contract is with them, no-one else, and they should sort it out if they agree the batch was faulty.