The only book like this that I have found is the Rune of Chaos and that makes runes seem like they are very rare.
I wrote that as a non-Glorantha introductory scenario to help people get started with the rules, not as anything to bind a scenario-setting by. I mean, if everyone made characters with magical professions for the game, there would have a bunch of runes around. It was just an intro scenario, and definitely not a binder to any set of setting rules.
How are you handling rune spells and cults in your game then?
Rune spells are as written in my game (integration, physical objects in hand, etc.), and my players group have been wandering Prax rather aimlessly for a while now - so other than being lay members, they have not really gotten into the cult lifestyle as of yet (except for villifying a possible NPC Yelmite). They are about to hit the city of Refuge and then have some choices to spend some civilised time around others, so I am thinking that some cult choices will be made very shortly.
Basically, in my game, the cults themselves do not hand out runes or anything. They have access to learn certain Rune Magic spells because of a general knowledge of it within the ranks of the cultists. How I run it is that the listed Rune Spells for the cult are not a license to automatically HAVE the spells, but the guarantee that the spell will be available to be taught freely to cult members who have the runes necessary.
Now, that might come as a problem for a few Gloranthans who dislike the idea of an anti-Chaos cult needing Chaos Rune(s) for certain spells taught by their cult. Although I did not make that decision in the design process of the cults books or original spells, I figure that it is because these cults are not as consumed by their battle against Chaos in the Second Age. Before you all grab your torches and pitchforks...hear me out.
Think of it. The Second Age is dominated by a different kind of threat besides just the growth of Chaos. The kind of Myth-altering strangeness that the God Learner/EWF wars represent could easily dominate the worries and tecahings of some cults. Chaos is always there, and it must always be battled, but in a world where one empire is erasing and re-moulding gods while their enemies are trying to awaken the Dragon within a continent...maybe a cult's devotions are a bit askewed?
Also, we all know that Chaos is really strong in the 3rd Age. Maybe it was the mistaken practices of the Second Age cults that helped strengthen it? Maybe the people of Glorantha are generally ignorant of the potential hazards of integrating a Chaos Rune? One does not turn to metal when they integrate a Metal Rune, die when they integrate a Death Rune, or turn into a zombie if they integrate just one Undeath Rune. Perhaps it is the "just one Chaos Rune never hurt anybody, but check out this cool spell I can learn now!" mentality in the Second Age that turns Chaos into such an omnipresent threat in the Third Age?
I'm not saying any of this is law or anything, but I am saying that it
could be, and if it helps make your 2nd Age game feel better and make more sense...then maybe go with it.
As I've always said; it is better to look for why a rule might be right than automatically assuming it is wrong.
Hope that is helpful...and cheers all!
-Bry