You can download OpenStreetMap data for yourself for any part of the world and, providing the data file is small enough, convert it for use with RiscOSM using our free OSMConvert tool:
OSMConvert 1.10 (228k)
For the British Isles, the conversion process takes 47 hours to run on a Pandaboard, but is rather quicker on an iMX6, IGEPv5 or Titantium. Smaller areas, e.g. counties, can be converted much more quickly.
Main RiscOSM page