Buying combs can be a problem. I currently need a plastic comb to go in my back pocket (to deal with the little hair I've got left) but supermarkets only seem to sell them as part of a pack of lots of different types of combs (which I'll never use) and discount shops tend to sell those which are made of really brittle plastic (which break in my back pocket as soon as I sit down). Getting hold of a single, slightly-bendy, plastic comb is almost impossible.
However past experience has taught me that independent pharmacies are usually the best place to look, so that's where I'll be going to see if I can find the type of comb that I'm seeking. I suggest that they're probably also the best place to seek out steel (or aluminium) combs, so perhaps you might try there?