So...after I posted my list, I thought I would check back on the Pulp Magazine Archive to see if any kind souls had uploaded more since I last downloaded some only-ever-published-in-magazine stories (a few years ago I realised). And I found another 32!
I really should sort them all out. I had plans to print them out and bind them in a book but that hasn't happened.
Anyway, it now means I only need the following to collect everything (at least everything SciFi) that he wrote:
Travelers - Amazing Stories Sum 1999
The Observatory - Amazing Stories Sum 2012
The Election - Analog Mar 1983
Come Into My Brain! / Menace from Vega / Voyage to Procyon - Imagination Jun 1958
Pluto Story - Nature Jan 27 2000
Hail to the Chief - Omni Nov 1984
The Catch - Omni Aug 1990
The Last Surviving Veteran of the War of San Francisco - Omni Mar 1991
Hot Times in Magma City - Omni Online May 1995
Galactic Thrill Kids - Super-Science Fiction Apr 1957
The Happy Sleepers - Super-Science Fiction Feb 1958
Prison Planet - Super-Science Fiction Feb 1958
Planet of Parasites - Super-Science Fiction Apr 1958
A Planet All My Own / The Cold-Blooded Ones / A World Called Sunrise - Super-Science Fiction Aug 1958
The Aliens Were Haters / Exiled from Earth / The Unique and Terrible Compulsion - Super-Science Fiction Dec 1958
Re-Conditioned Human / Waters of Forgetfulness - Super-Science Fiction Feb 1959
Plus a bunch of horror stories:
The Unbeliever - Magazine of Horror Aug 1963
The Man Who Believed in Werewolves / Dig That Crazy Scientist - Monster Parade Nov 1958
Find Me a Victim / Secrets of the Torture Cult / Coffins Are for Corpses / Crossroads of the Ghouls - Monster Parade Dec 1958
Demons of Cthulhu / The Thing Behind Hell’s Door - Monster Parade Mar 1959
The Undertaker’s Sideline / You Can’t Cheat Death’s Demon - Monsters and Things Apr 1959