Just need it as backing for a map, basically summat to stick drawing pins into. Tried Hobbycraft but they don't do it.
Sounds like a job for PVC foam board. </p> http://cgi.ebay.co.uk/White-Foam-PVC-Board-3mm_W0QQitemZ260349400870QQcmdZViewItemQQptZLH_DefaultDomain_3?hash=item260349400870&_trksid=p3286.c0.m14&_trkparms=72%3A1301%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318</p>
I've seen this in sheet form at Staples. But try Howarth Timber they used to sell it. Failing that you could use a fiber board, will do the same job, Howarth sell that also.
Simple. Use the skin of a poorly Romanian orphan. Ideal for the job. Failing that - don't bother putting the map up at all. That's probably the easiest solution. Glad to be of assistance.