New aerospace industries would have been founded by whatever personnel from Stonewell/Bellcom/Shinnakasu were on site when Macross initially fold spaced to the edge of the solar system.
Indeed. The remnants of Stonewell, Bellcom, and Shinnakasu were merged into a new manufacturer called Shinsei Industries. The other major competitor for the New UN civilization is General Galaxy, which is actually a Zentraedi start-up.
Anyway, as for the original Sv-51, it was apparently built in a joint effort between Sukhoi, Israel Aircraft Industries, and Dornier (it isn't clear whether these companies were part of the Anti-UN Coalition or if the design was stolen from them by said coalition). According to expanded universe materials, the Sv line was not canned completely but was reabsorbed by Shinsei Industries following the Zentraedi War, and they've continued to tinker with the design even if it's never become their main product (they used a few such jets in the filming of the in-universe Macross Zero movie in Frontier, for instance). The Draken III's in use by Windermere are Sv-262's, which I'm guessing they stole during their independence war.