I would like to read the myths as prep for heroquests (I think I'm past due) but I'd rather read them not in-game. Is there a resource for this?

Some of them have been reprinted in Gloranthan works available at http://moondesignpublications.com though I don’t have an index for that…

I don't think they've been published anywhere else than official Glorantha sourcebooks (I have some of the Finnish editions from late 80's or early 90's), but I might be wrong.

Even then, I doubt all the myths would be there in a convenient package, so I'm afraid you are stuck with in-game text.

EDIT: Whoops! Misread the dates and answered quite an old post, sorry.