If we´re talking purely about guilds that have magic as main focus, Kirin Tor Intelligence comes to mind.
If you want to RP a warlock, there´s cross-faction Legion cultists Cleft of Shadow/Ashen Wake.
Then there are plethora of guilds that utilize magic a lot (for example the one I´m in), but has primary focus on other things, so it doesn´t really come up in any recruitment threads or posts.
When it comes to Argent Archives updates, there´s a one pretty big problem with it: You need to manually change something in your guild page for it to be viewed as an update. So unless the GM keeps in mind to bump their own guild page on AA, it falls into obscurity.
There are guilds out there that have not been updated in over half a year, yet are still active and I have interacted with them even in the past week.