IIRC, aside from government surplus auctions (which is an easy way of getting 3 dozen if you pick up on site), I think the right keywords to use are “shock mount” and some variations on military surplus, rack, case, etc.
Local pickup is the key for these things - anyone living near a major metro should inquire where the state/county/city auction location is (though sometimes they auction “in place” so pay attention).
I got something like 6 steelcase filing cabinets for $160 - even renting a truck to pick them up was still a huge savings.
I got something like 6 steelcase filing cabinets for $160 - even renting a truck to pick them up was still a huge savings.