The orc pantheon never really had anything written about them for most of 1st edition—same goes for almost ALL divine realms, for whatever reason. We always skewed toward how a deity's worshipers functioned and spent less time on the actual deity's relationships and home for most of 1st edition out of a notion that folks preferred that wordcount to be about how their characters are affected rather than about content that doesn't actually affect a character—in other words, we skewed that information toward the player and not the GM.
That's something that we finally were able to start addressing and changing only relatively late in the 1E life cycle, in "Planar Adventures." There, I worked with the many authors of the book as the lead developer to make sure to include information about as many divine realms as possible. For the orc pantheon, that meant they ended up in the Maelstrom, not the Outer Rifts, on a continent-sized realm called Volkorgoth. My take (and this might not be current, since I'm now focused on the adventure side of things and not the lore side so much) is that the orc pantheon's realm remains on the Malestrom in Volkorgoth, and that the shake up of who's in and out of the pantheon would have manifested in Volkorgoth as a deity-level, over-the-top sort of restructuring of borders and terrain and themes and all of that. Volkorgoth was always meant to be a place where all the orc deities would dwell, regardless of their personalities, in a sort of echo of how different orc cultures on Golarion all live on the same world.