Look in the local paper, ask your mates for a curtain maker locally. Curtain makers always know a fitter and where to get the poles. Much better to get them made to measure. Otherwise Laura Ashley very lovely, expensive though.
John Lewis have lots of poles, also places like Dunelm Mill (cheaper). I would have them made by a local curtain maker rather than use their services, though - have heard they're not so good, same goes for Laura Ashley.