Rack ears aren't all necessarily the same size for each piece of gear. By this, I mean the part of the rack ear which joins onto the side of a unit. Some rack ears need to have little bevels and little checks out of them to accommodate quirky little fittings in order to fit properly. You'll need to be carful and look at the sides of your units well before knowing exactly what to get.
Best thing would be to come by them from the manufacturer of the particular piece of equipment. Or, go to a metal worker with the gear and a specimen ear from another rackable piece of equipment highlighting that you want 'this' but to fit onto 'that' particular unit.
Alternatively, use rack trays with the gear.
Hope this helps
LiD