Baggins do have an online presence http://www.bagginsbooks.co.uk/ but no mention on there of maps. As I say, I know they usually hold a large stock of old LR and EX OS maps - might be worth giving them a call with your specific requirements?

I'm not due down that way for some time (went a few weeks ago), otherwise I'd suggest giving me a list and a price guide...

(It's handy for the Medway sites, if you fancy combining the trip!)