Non-gas lift office chair (Canworthy Water PL15)

My office chair's gas lift has failed after a short time (out of guarantee, unfortunately) and I've been looking for one of the old reliable traditional 'screw adjustment' chairs. Nobody seems to sell them these days. If anyone has got one in usable condition I'm interested, or if anyone can suggest a local ex-office furniture outlet that might have one I'd be grateful. Thanks. Fed up of planned obsolescence. :)