Highway Hunter was, for all intents and purposes, a Spy Hunter clone with way more weapons. The story made zero sense (you were supposedly "saving the world", but in the end, a short cutscene shows you driving toward the open road - seemingly leaving humanity to be destroyed... good times), and the enemies fit about three basic templates (run into you, shoot lasers at you, or shoot what looked to be rocks at you), but the game itself was kind of fun. It's a nostalgic game, of course, meaning that if you haven't already played it, there's next to no point in hunting it down now, but the music was classic old school MIDI game music. As far as I know, Serge Shishkin hasn't done any other game soundtracks - which isn't surprising, the company that developed the game (Omega Integral Systems) only made Highway Hunter.
I've downloaded Highway Hunter and ripped all the music from it into MP3 form. The bitrate is intentionally low (it's MIDI, after all - nothing is lost at 128KBPS). As far as I know, this is the only copy of the actual soundtrack online, so have at it. It's your soundtrack to killing strange alien bosses while they chuck little red blobs at you, all the while wondering why exactly the ridiculously inferior M-Laser is the final weapon upgrade, and why the almighty P-Laser ends up with no ammo as a result.
Download the full soundtrack here.
Please note: it may look like some of the tracks are missing (i.e. The Lost Roads 2), but for some reason a couple of the levels borrow tracks from previous levels. It's all here.