Suave - haven't seen anything that size - I know Homebase do the bog standard ones - I've got some in my office. They are nowhere near strong enough though - they bend with a few lever arch files on!
Have you considered using studding or round bar? You could get the appropriate size (say 15mm?) and resin anchor them into the wall - that would certainly be strong enough.
Screwfix sell the
studs and the
resin - though having seen what they're charging for the studding - you could probably save money by improvising via a local scrap yard.