UK Walkers Roasted Chicken Crisps
Sometimes you can get them on Ebay. Otherwise, there are many sites where you can order them on-line. (thebritishshoppe, britishdelights, englishteastore, britsuperstore, britgrocer, jollygrub)
There used to be small Brit stores in both Freighthouse Square in Tacoma and on Gilmore in Issaquah but I don't know if they're still there. I do ALL of my shopping on-line these days.
Maybe you could post a message on the Chowhound England site and see if someone would ship them to you directly. :) You might make a new friend to trade items.
I understand the craving--Walkers are great (their salt and vinegar were my fave). This isn't exactly the answer you wanted but I find that there are brands of chips in Canada that are similar to Walker's-you can get roast chicken flavor, steak and onion, ketchup, etc etc. So if you are planning a trip to Vancouver or Whistler, check out the chip section of a grocery store--you might find something you like almost as well.