From the lead OpenTyrian dev on IRC:

<Mindless`> Flandry: the official "it's freeware" message is here --> http://www.freewebs.com/worldtreegames/
<Mindless`> Jason never got around to putting up a non-2000 version on that site
<Mindless`> but he gave us the Tyrian 2.1 source code to port because he didn't have a copy of the 2000 source (probably gone when his house burned)
<Mindless`> Jason has no problem with 2.1 (and probably older versions) being freeware
<Mindless`> but he doesn't want to give away his right to/ownership of the game entirely, so it'll probably never be Debian-free
<Flandry> oh
<Flandry> so no packaged data :/
<Flandry> ok, thanks
<Mindless`> technically the freeware license is "play it all you want and share it with friends"