Wheelbarrow - if you want a small one then go to B&Q/Homebase they are about £30 ish. If you want a big one (200L) then look at ebay (I think it is called Atlantic something).
Mucking out tools, if you are ordering other stuff then most of the shops like Robinsons, DH, Horseloverz etc will have them otherwise to save postage just get from local tack shop (there wont be much in the price). Brooms etc get from B&Q/Homebase etc.
Try maybe somewhere like Surrey Equestrian or for the wheelbarrow try www.greenfingers.com- I got a huge plastic one there v cheap and theres a few to choose from.