So I thought "No, we can't find any" but put into eBay '2 foot square perspex' and after a few more clicks ended up buying a piece which will need cutting down somewhat and drilling but is free delivery. All the pieces I found yesterday were about £8-£10 but cost about £40 postage. This item costs £8 summat and is free postage!!!!
And hopefully eBay covers you so it should arrive!!