The AIDS-stricken father of a missing 9-year-old boy urged his ex-wife to return him so that the child could "have some time with his father before it is too late." Artie Wallace, 32, of Santa Rosa choked back tears as he told a news conference that his ex-wife, Julia Louise Wallace, 30, took their son, Shawn, on Aug. 3. That was the day before the scheduled beginning of what may be the nation's first court battle for custody of a child by a father who has AIDS. Shawn and his mother were living in Apple Valley at the time of their disappearance. A warrant has been issued for the mother's arrest by the San Bernardino County Superior Court in Victorville.