Do you mean the H&M ones, specifically or just square cut briefs in general.
If specifically, you can go directly to H&M as most of them sell the same items worldwide.
If in general, you can go to anyplace that sells contemporary men's clothing and also find square cut briefs. Sears, JCPenny, Macy's, Loehmann's, Century 21, TJ Maxx, Marshall's, Old Navy, GAP...I could go on, but I'll spare you.