Sony SRF-40W FM Walkman - Billboard Article from 1981
As mentioned in the main article on Sony Walkman radios, as well as my review of the Proton 100, high-fidelity-oriented publications such as Audio or Stereo Review didn't give much coverage to Walkman or similar units. Billboard provided some coverage, though, on page 62 in its May 23, 1981 issue (fair use excerpt), announcing the introduction of three new Walkman models. Among them was the SRF-40W, Sony's first radio-only Walkman, highlighted in the article above.
As I mention in the main Sony Walkman radio article, note the suggested list price of $90. The equivalent cost in 2020 would be more than $240!
Also note the mention of the headphones, included with the unit. Apparently those headphones could be easily lost. Most present-day eBay offers of SRF-40W units don't include the headphones. That doesn't really matter; the SRF-40W's audio outputs can easily drive most headphones.
I haven't found other Billboard articles about the early Walkman radios. Similar publications such as Radio and Records did not appear to have much coverage.
The site americanradiohistory.com offers a wealth of material, not just about broadcasting, but related businesses as well. That's where I found this article. Respecting the wishes of the owner of the site, I'm not linking directly to the article displayed on this page. The date (May 23, 1981) and page number (62) will be enough for you to find it if you wish to do so.