SRDS also had (or has) editions for media buyers in print media and television. In the market that I was in, it was business to business media (trade publications), The company I worked for was the largest in the industry with 134 titles in the U.S. Which is why bought the space taking up the spine of every issue. We were in LOTS of markets....including more than a half dozen titles for engineers at Electronics Industry OEMs. All of our 11 editors were engineers with EE degrees and industry experience, One of them, Dan Strassberg, was active on these boards. Unfortunately, Dan left us about 10-12 years ago.There are a few Spot Radio Rates and Data from SRDS at SRDS - Spot Radio Rates & Data media buyer guide
I have tried to get more issues, but can't find them anywhere!
I've seen various SRDS directories in larger Public Libraries. You might want to check out libraries near you to see if one has what you're looking for.