Here are 17 mid 1920 issues of the AIEE magazine which was the premier magazine covering the engineering aspects of power transmission, generation, motors, etc. These are each packed with advertisements including many insulator manufacturers (Lapp, Locke, GE, Corning, Etc.) All are in decent condition -- Example Pyrex ad is shown.

Issues are 1926 -- January through June, October-December (9 issues) 1927 -- Jan, Feb, May, June, Aug, Oct, Nov & Dec (8 issues)

Free to anyone if they pay actual shipping -- these are pretty heavy but USPS media rate is quite reasonable.