I've used these guys for repair/service of my Pentax 67's, good service and not outrageously expensive. http://www.asahiphoto.co.uk They're based in Brentford so I was able to drop off and collect in person so I'm not sure what their postal costs are like.Miles W can have a backlog, but he tends to be cheaper than Newton Ellis.
For any difficult serious Pentax repair, Harrow Technical are probably the most experienced people around, but typically charge more than your average independent repair person.