Went to another chemist's today, and got told that it's clobutinol(sp?) that was taken off the market, not dextromethorphan.
She also said the tablets I wanted contained cl. rather than d. (which is odd, since they were listed on the mail-order site when I searched for d.); she had the lozenges I had had before, though (though in a slightly different packaging) as well as syrup, so I went with that since sucking the lozenges takes about a quarter of an hour and I found that annoying.
So now I have my sweet, sweet psychoactive drugs! Hopefully that'll keep me from coughing again this night.