Is there an official Ulgrotha map?

Sure, just look at the Homelands expansion symbol

On a more serious note, I think the Homelands comic (which can be found online at MTG Salation) shows some of the landmass as seen from space, and it's probably worth checking if there's a more detailed map somewhere in said comic or in the Homelands Document.

There you go. The thingy where the lines are pointing to must be Castle Sengir. Other than that we do not know where everything is located. Although since we know Koskun is next to the Barony, and Autumn Willow's woods lie between Aysen and Koskun, it seems as if the five main locations are situated in color-wheel order.

Mm, this doesn't help me much, but thank you. If Ulgrotha is indeed arranged as the colour pie is, though, then I have something to work with.