In my experience.. anything you want to find is now pretty much impossible to find.
Your best/only option is to farm something else and trade for what you want. I needed Proto Heat Radiators.. these should be easy.. HGE in Boom. But the way USS are done now, the chances of finding the signal you want in the state you want are very slim.
What I did instead was I found a HGE in the system I was in. I dropped in and it was full of Core Dynamics composites and Proprietary Composites. I don't need either of these things, but in the 30 minutes the HGE lasted, I was able to log out/in and farm this thing until I had hundreds of each of these. I then jumped over to a Material Trader and traded them in for Proto Heat Radiators. I was able to trade for about 40 of them after about 25 minutes of farming, that's a better rate then when I used to look for the correct source.
In my opinion, the easiest method of getting anything now is to just farm something you don't want/need and trade it. Yes, they trade at 6/1 ratio which sucks, but if you have 130 of a material you don't need.. it doesn't really matter.