The only Ability to automatically set Hail is Snow Warning -- which, as you said, was introduced in Gen IV. As there's also no natural hailstorms in the Gen III games, the only way to get hail in-battle is to use Hail manually, unfortunately.
Hailstorms (Bulbapedia)
It should also be noted that prior to Gen V, Sturdy only protected a Pokemon from being OHKOed by the four OHKO moves, rather than acting as a Focus Sash.