Colchester striker Vernon has joined on a month's loan after he slipped behind Clive Platt, Kevin Lisbie and Kayode Odejayi in the pecking order at the Community Stadium.
Stimson has also swooped to sign 19-year-old defender Fry on a one-month loan deal from West Ham.
Both players are set for starting roles as the Gills aim to bounce back from Monday's 2-0 defeat at Brighton.
They came through that game with no new injury concerns but Adam Miller and Gary Richards look set to make way for Vernon and Fry.
Midfielder Danny Jackman (dislocated shoulder), centre-half Simon King (ankle ligaments) and striker Mark McCammon (hamstring) all remain sidelined.