(Scratches head)...Thats a good question.We do have a thread called "Where to find scrap",but I don't think any of us have discussed commercial equipment/material.I lucked out in getting my material.I have owned a tree service for 17 years in cocoa florida(Nasa Capital).Most of my customers are employed by nasa,or ones of its very many contractors.So in my case it was just a matter of letting my customers know what I was doing and the material started pouring in.2 years ago,the son of one of my customers called me to inform me that Lockheed Martin was stripping a Navy Destoryer and we were entitled to all of the equipment that was to be disposed of.Of course we had to prove a few things,and make a few promises,but the sheer volume of equipment took us about a week,and about 10 loads(in a very large trailor,just to transport all of the equipment about 20 minutes away.Some of the older members saw the pics of the equipment.I still have 100's of pounds of boards just from that endeavor,including,port and starboard sonar boxes circa 40's or 50's.
Unless you had a large company I doubt you would have luck finding equipment like that on a large scale.And of course as time goes on,the material from that era gets less and less,and the newer stuff has less and less gold on it.