I think they may have discontinued the salt and vinegar ones, I asked in Asda last week because I wanted them too and the lady said they hadn't had any in for months and weren't getting any more in
The last place I saw them was in poundland/stretcher about 2 weeks a go, I'm guessing they still have stock left from Summer so you could try there.
They definitely don't have any in my local poundland or home bargins but i will definitely take a look in £stretcher. thanks! They were the only flavor I liked and being 4 syns were a lot less than monster munch.