I use the D&D minis when I can. Otherwise I use the tiles from the Shadizar and Messentia box sets.
Most of the battle should be taking place in the PCs minds, the minis are just there to make sure everyone is on the same page rules wise, so I don’t exude to much effort trying to track down representative minis.
The Sessair and Drune Celts fromRackham have some great figsd for Cimmerians and Picts. Reaper has plenty of nordic types as well as knights and such. The GW Brettonians and Empire as well as some of the Dogs of War are all a good fit for Hyborian kingdoms and War Gods of AEgyptus likely has some nice Stygian-style figs. I haven't looked at them but it seems logical.