MBW has a limited supply of cushions, mats etc., bought with donations. It is always helpful if participants can bring their own cushions etc.
MBW has no special connection with any of these suppliers, but it might be worth while looking there for what you need:

Natural Living
http://www.naturalliving.co.uk/acatalog/index.html

Various meditation supplies
http://www.windhorse.co.uk/

Incense, etc.
http://www.buddhistsupplies.co.uk/

Cushions, mats, etc
http://www.yogamad.com/

Cushions, stools, timers etc
http://www.bluebanyan.co.uk/