DriveThruRPG.com has PDFs of several of the more recent Heroquest/HeroWars books, including the main HQ rulebook.
Of real note is the HeroQuest Hero’s Book. This skinny little ‘intro’ to the HeroQuest rules covers all the basics of the game system and provides a number of example characters, almost ready to play — said examples are Glorantha-setting specific, but still provide good examples of how to do character’s (especially magic-using chracters) correctly. As a primer on HQ, or as the ONLY book you need to ‘get’ about 95% of the rules in the game (as long as someone ELSE already has the main HQ rulebook) it’s perfect.
And it’s a five-dollar PDF download, which is a pretty darn good deal.
If it seems likely that I’ll ever trick you into playing HeroQuest in any setting at all, I recommend this.