I just recently found out that JMS wrote 3 short stories about B5 - one of which told the story of Lyta & G'Kar.
Actually, JMS wrote four of the six short stories. You could try to find them in a major library, I guess. Other than that, there's eBay.
Maybe JMS could be convinced to put his four in the upcoming script collections???
<u>SHORT STORIES (all out of print, both magazines out of business): </u>
Title: The Shadow of His Thoughts
Author: Straczynski, J. M.
Timeframe: 10/2262
Ss_pub_in: Amazing Stories
Ss_issue: Summer 1999, Number 597
Ss_commnts: The Londo Story
Title: Genius Loci
Author: Straczynski, J. M.
Timeframe: 01/2263
Ss_pub_in: Amazing Stories
Ss_issue: Winter 2000, Number 599
Ss_commnts: The Lyta / G'Kar Story
Title: Space, Time, and the Incurable Romantic
Author: Straczynski, J. M.
Timeframe: 2560-2592
Ss_pub_in: Amazing Stories
Ss_issue: Summer 2000, Number 602
Ss_commnts: The Marcus / Ivanova Story
Title: Hidden Agendas
Author: Straczynski, J. M.
Timeframe: 2262
Ss_pub_in: Babylon 5/Crusade Magazine
Ss_issue: May 2000, Number 22
Ss_commnts: The Ivanova/Warlock Destroyer/Ulkesh's Vorlon
Transport/Sheridan/Lyta Story
Title: True Seeker
Author: Avery, Fiona
Timeframe: late 2269
Ss_pub_in: Babylon 5/Crusade Magazine
Ss_issue: July 2000, Number 23
Ss_commnts: The Narn Story (carries on from episode 17 "Legacies"
http://www.midwinter.com/lurk/guide/017.html )
Title: The Nautilus Coil
Author: Keyes, J. Gregory
Timeframe: 2263, or maybe even sometime in 2264
Ss_pub_in: Babylon 5/Crusade Magazine
Ss_issue: August 2000, Number 24
Ss_commnts: The Garibaldi/Lyta/Psi Corp/Vorlon story. Connects with "Dark Genesis - The Birth of the Psi Corps"