Astral runes may not be crafted via the Abyss. There is no talisman needed to access the astral altar; the astral altar, along with the Blood and Soul altars, are the only Runecrafting altars that do not have a talisman associated with them. However, the Blood and Soul Runecrafting altars can be reached through the Abyss, unlike the Astral altar.
Astral runes may also be purchased at Baba Yaga's Magic Shop, located north of the bank on Lunar Isle. The shop stocks 250 astral runes and is located in a moving house with bird legs on it, walking east and west. Players must have a Seal of passage with them when attempting to trade with Baba Yaga or they'll be thrown off the island.