I share your concerns retailpharmacist, the quality does vary..
Having been a weekend locum myself in the past, I find it very hard not to do a good job when you are there, as you always get called back for your good work.
I am also looking for locums near Redhill, Surrey myself for my friendly village shop for regular weekdays, please PM me if anyone is interested.
I would say that many of the better ones will be booked up a lot more than a couple of weeks or so ahead.... my diary was solid 3 months ahead, a fair bit to 6 months and a few re-booked annual leave people who would book me a year ahead.
Maybe try asking other local pharmacies for their contacts; the LPC and/or Soc Branch Secs used to keep locum lists and although they don't officially any more, might be able to point you the right way. Attending Branch meetings, CPD events etc and talking to people is good too (tho maybe too late this time).