On the subject of used bookstore chains, the only one I know of here in the states (or at least in my part of the country) is Half Price Books, and I've only found Archie Comics there once (I bought a bunch of digests for $1 a pop the one time I did find them there). Most of the time they just have back issues of various DC and Marvel titles (and the like) - all the "popular" titles that people supposedly want to buy these days (I've never gotten into Marvel or DC and don't understand why those have so much more of a following than Archie does).