I have seen fewer and fewer race restrictive guilds as time goes on. I do not want to say there are no Orc Clan guilds, but i cant recall any by name. As others suggested, poke around the guild faire and the forums.
I feel inclined to give a mention to the guild I participate in, the Blackheart Accord. Since cross-faction guilds/communities have been added, just about any being is able to join in terms of lore/RP. If you can explain it, it can happen for the most part- including “Alliance” races. Here is the link to their recent forums post if you wanted to look at it further.