Okay, so that's definitely more sea-related traits rather than inland. I see two possible ways to run with this:
1) The Asar live on the coast. It does put them outside the main travel zone, but we can make individuals playable as immigrants in Kothinar/Okudan/Rasumbel, and Vishaza itself the point of first expansion. They would be about as far from Rasumbel as that polity is from Okudan, although there are more mountains to cross on that side.
I do want to put a thing on the coast at some point, but I am thinking of that as an expedition/discovery scenario — possibly even a settlement founding, someday. Something plot will involve the coast eventually, anyway.
2) Vishaza remains sited in the prairie pothole region, but the Asar who founded it immigrated from somewhere coastal, either the southeast coast (past Rasumbel) or… wherever else, perhaps the northeast whence the Okudani came. In any case, I would suggest they immigrated before the Okudani.
You would still not have the tidepool and shellfish farming environment in Vishaza's marshes, but there is potential for future expansion opening up a different population of Asar in their original native biome. You could have some interesting ramifications regarding saline vs. fresh water in the potholes, and the Asar's compatibility with and regard for different water conditions in the prairie marsh. There's an outside possibility that the Asar could have brought some kind of estuary shellfish over with them and coaxed it into surviving in certain pothole conditions — probably not thriving and not their chiefest food source, but say they held on to the practice as part of their original traditions.
You also have the makings of an epic saga there, if these sea-adapted people struggled their way over the mountains a few centuries back…
There's also the trivial solution:
3) We take the Asar out of Arbannin altogether and plan them into the second nodal region, on the northeast coast — the area where the Okudani came from. Doing so would most likely make the race unplayable until that expansion happens, however, or at least until we got the first region well-established in terms of plots etc.