PRG might well have some of the early
stock they inherited from either
Production Advantage or from GSD.
I caution you that when I priced them used about 5 or 6 years ago, they were running about $1700 per tower, for a roughly 7ft high single width tower that was stackable - I.E. they had corner plates installed to
bolt together as taller units.
These units are designed to hold 5 S4 ellipsoidals each, typically, on a
channel steel frame (
Kindorf, Uni-Strut, Versa-Bar) that allows vertical adjustment as well as front/rear movement, of the
unit hanging position.
I think one of the reasons the aluminum units were so expensive, even as used, is they are not cheap to manufacturer in the first place, as well they really don't go bad over time, so no real reason to sell off, as any new
unit would cost even more then the initial units.
Due to the cost of the used aluminum units, I opted to have a local steel company weld mine to a custom design. 8 towers cost $4000, plus add'l for the internal channels steel, mounting hardware and cable bundle assembly. Due to the weight, I did not design nor equip these to stack, but that was not a requirement at my space.