While there isn’t currently a notable Dark Iron guild, to my knowledge, the dwarf community has a good number of Dark Irons and guilds that accept them. Dark Irons and the other dwarves have had a shared government for quite a few years now.
Here’s the Mead Hall info, which is that dwarf community. Come on by and have a chat, and I’d be happy to help you find a spot in one of the dwarf guilds.