Hedderly promoting the 28g in Western Field October-November 1911; "The Gnat Gun Does Good"
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA485&dq
There is an image one page back of Hedderly with a 28g Parker
https://www.doublegunshop.com/forums/ubbthreads.php?ubb=showflat&Number=597585&page=3

Each subsequent issue has another "The Small-Bore Shotgun" article if you want to scroll down.

Part 14
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA519&dq
Part 15
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA137&dq
Part 16
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA212&dq
Part 17
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA310&dq
Part 18
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA411&dq

Ad for 20g Parkers January 1912
https://books.google.com/books?id=7SQPAAAAYAAJ&pg=PA183&dq

He was still at it in the September, 1912 issue, Part XXIII - A "Twenty-Gauge de-Luxe"