Ooh I think I have some at work. What size do you need? (Edit - just read the title for the size)
Ill take a look tomorrow, measure up and take some pics for you. I have several lengths, we can do a cheap deal. Unless you find a local supplier of course.
30mm x 30mm with a 6mm slot possibly about 3m total.
Spoke earlier to a company who have a picture on there website but don't actually sell it as it doesn't exist in there catalogues