By a commodius vicus of recirculation i happen to have come across two pairs of Apollo mixing desk legs - retail at about £500 a pair! They are nice - about as good as you could ever get!
The are reasonably heavy, about 10Kg each so postage could get gnarly, they have been used so there are marks on them but nothing terrible, complete with aluminium side plates. They are really only suitable for larger mixing desks. I would say at least 500mm wide - anything less than that they are going to look silly. They are about 580mm high and the base from back to front is about 840mm. I can get exact measurements if required.
I can also get the top steel cross section that sits on top between the legs and your desk made to measure to your requirements.
They will be very reasonably priced, but it will depend on how much work you want doing for the top braces.