Forestan, Foreston, Horeston, Sorestan, Soreston
According to the Vulgate, Sorestan borders Norgales "par evers" Sorelois. It's uncertain whether this means Sorestan was between Surluse and Norgales, or Surluse between Sorestan and Norgales, or both Surluse and Sorestan bordering Norgales; the last is more likely, and Sorestan be approximately the rest of Chester excluding the peninsula proposed for Surluse.
In Vulgate V, Morgan, Sebile, and the Queen of Sorestan kidnap Lancelot. This seems to be the episode Malory gives in Boox VI, although Malory has four queens: Morgan and the Queens of Norgales [Norgales], Eastland, and the Out Isles. It seems likely that the Queen of Sorestan should be identified with the Queen of Eastland, and, thus, that Malory's Eastland is the Sorestan of the Vulgate.
Malory's Eastland, on the other hand, might for convenience's sake be considered separately from Sorestan. Using this theory, Lincolnshire might be called Eastland. Or the name might be given to the easternmost bulge of the island, including Norfolk, Suffolk, and Essex (which name, of course, derives from "East Sex"). Eastland might, indeed, include all the counties listed as raised by Mordred in Malory XXI: Kent, Southsex, Surrey, Estsex, Southfolk, and Northfolk, which would all be sub-subkingdoms.
Eastland, Queen of
In Malory, the Queen of Eastland, Morgan, and the Queens of Norgales and the Out Isles kidnap Lancelot and take him to Castle Chariot (Cart Castle), whishing him to choose one of them for his paramour.
From this and other evidence, I suspect Eastland to be identical with Sorestan; thus the Queen of Eastland is to be identified with the Queen of Sorestan. Incidentally, the reputations of the Queens of Eastland, Norgales, and the Out Isles as dames of magic seem to rest - as far as Malory is concerned - on their association with Morgan and on Lancelot's assertion that they are all four "false enchantresses".