There are no stablemasters in any Starter Island Zone. This goes back to the time when Starter Islands were just that, and you had to leave them to get to the first city where you could get a horse for the first time.
However, with the system as it is now, I would support this idea. Stablemasters need to be introduced in all larger towns/cities that don't currently have them:
- Port Hunding (Stros M'Kai)
- Stonetooth Fortress (Betnikh)
- Mistral (Khenarthi's Roost)
- Bleakrock Village (Bleakrock Isle)
- Dhalmora (Bal Foyen)
- Northpoint (Rivenspire)
- Kragenmoor (Stonefalls)
- Bergama (Alik'r)
- Kozanset (Alik'r)
- Redfur Trading Post (Grahtwood)
- Dune (Reaper's March)
- Kragenmoor (Stonefalls)
- Narsis (Deshaan)
- Alten Corimont (Shadowfen)
- Fort Amol (Eastmarch)
- Nimalten (The Rift)
I also think that everywhere that has a stable should have a banker as well.