Strictly for the Warband scene, it’s dwindled a liiiiiiittle bit with the end of the ‘Fourth War’. While there’s still a few ‘Warband’ type guilds, Path of Glory is a strictly Pro-Horde Anti-Alliance Warband. They do take all races, though I understand a majority are Orcs.
If you’re looking more for a ‘Clan Experience,’ both Orcs of the Red Blade and the Iron Wolf Clan are a good place to shoot. While the Orcs of the Red Blade fit more of the traditional ‘Old Ways’ clans of pre-Outland Draenor, the Iron Wolves are a warband-turned-Clan built on a post-Garrosh world. The former is strictly Orcs only, while the latter allows Orcs, Tauren, Trolls and Vulpera into their ranks (no Elves/Forsaken). Both are fantastic groups to RP with!
There’s a number of multi-racial Clan guilds, the Frozen Paw Clan included, that do accept all races and types while keeping to the Orcish ways. Those three above are who I’d definitely recommend for a ‘Mag’har’ worthy run!