You can buy it directly from GOG.com for approximately $5.99 .
Digital activation keys for GOG can sometimes be found on retailers like Gameseal or Gamivo for as low as $2.00–$3.50 . Technical Guide for GOG Version Warhammer 40,000: Fire Warrior Free Download (GOG)
The GOG version is optimized for modern hardware but may still benefit from community fixes: Warhammer 40000: Fire Warrior - GOG.com You can buy it directly from GOG
A "Classic" version was recently re-released on Steam as of April 2026. Warhammer 40,000: Fire Warrior Free Download (GOG)