Here's some information gleaned from an exchange between an anonymous
player and Verant Game Designer Geoffrey Zatkin:

Anonymous: Out of a team of over 40
people there is 1 rune of frost.

Geoffrey Zatkin: The runes for ice
comet are found in places other than on
the dragons. They are found just like
other lvl 49 runes - we just also
threw them so that they would, in
addition, frequently pop on the dragons.

Anonymous:What about the other rune of
Astral? It hasn?t been found yet.

Geoffrey Zatkin: Sure it has - we have
people with a few of them. (person on my server
has it I think .. not sure)

Anonymous:Add a buyable lvl 49 DD
spell that does between 800-900 damage for 300
mana.

Geoffrey Zatkin: Something like this is
going in next patch.

Anonymous:Make the runes of frost and
astral just a tad more rare then the others,
and found off of mobs lvl 45+, not just
the dragons/50+ mobs.

Geoffrey Zatkin: Actually, they are
right now. (Good to know.)

Anonymous:Have the scroll of ice comet
found as a no-drop lore item that a SINGLE
group of lvl 45+s could get.

Geoffrey Zatkin: Going to be a quest for
this in addition to everything else. (very nice)

Geoffrey C. Zatkin
Arch-Mage of Norrath
Game Designer: Verant Interactive