Transactions of the Royal Martian Geographical Society was first a printed fanzine for “Space 1889” and then an online zine published by Heliograph.
Heliograph (re)published 3 volumes of the TRMGS material but the proposed 4th volume was never seen in paper.
*BUT* many of the articles are available online for free:
And *ALL* of Volume 4:
TRMGS Vol 4