Try these, but I have a feeling the price might be prohibitive.
http://www.earthboundlight.com/photo...-brackets.html
http://www.photomacrography.net/phot...irkbracket.htm
The cheapest way is to buy an off camera flash cable (Canon OC-E3) a lookie likey will do from Ebay at about £20, you can then hand hold the flash and still have a TTL exposure. It's the cheapest way to a macro flash experience and you will be able to use it for other types of photography