A crwth is not a small harp, if I'm not mistaken, but a bowed zither kind of like a square, non-lute-shaped fiddle. Is this what you mean? I'm pretty sure Mabsant used one on some of their early recordings. Rough Guide put out a pretty good Welsh folk compilation, which may have one. Siwsann George used one on her "Traditional Songs of Wales," which is a good CD. Sain records has a couple of compilations too which are worthwhile. But even among Welsh folk bands, it's not a common instrument.