I don't know how long you have been here, but Sainsbury's had those over the holidays last year (when more people buy frozen snack foods) and several other stores had them around that time, too. Not sure who else carries them on a regular basis, but I believe I have found them at Lidl and Aldi in the past, the Lidl closest to us has a bigger frozen foods section so they normally carry those and mozzarella sticks, etc.
For me the much bigger challenge is finding fresh jalapenos...

:\\\'(
I saw one pepper just once in a bag of mixed chiles, which annoyed me because I didn't want to have to buy several bags of mixed chiles to get 3 jalapenos.
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I should just read up on growing a pepper plant or something...