|Todd Stewart Contributor|
Normally I require some candles, a circle of salt, and a few goetic sigils written in blood, or coffee, or diet code red mountain dew. Any of that will do. But this time I'll make an exception I suppose. :D
I should point out that of the information on Aesdurath, that which doesn't appear in BotD3 isn't strictly canon. Obviously feel free to use it in your own games (and I'm humbled if you do), but Paizo has complete authority on the canon issue, and if it didn't appear in a printed source, it doesn't count.
A very large number of the Harbingers simply have no additional information written on them, because they began and ended with just a name, title, and the brief information that appears in the appendix in BotD3. Some of them have some brief write ups, while others appear in the next elsewhere in passing, but without dedicated information.
Zelishkar was mentioned in the 3.5 Osirion book, the PF followup IIRC, in BotD3, and had a very nice writeup in Inner Sea Monsters.
Hopefully we'll see more of many of them in the future, but such is Paizo's decision. If you want that sort of material, urge them politely and let them know your interest. I'd of course be gleefully open to writing about more daemons and other planar critters in the future (and especially daemons, proteans, and perhaps sceaduinars and jyoti too).
FWIW, I'm working on submitting a (non-canonical) story involving Vorasha for Wayfinder.