The Aces are the ECHL affiliate of the Vancouver Canucks of the National Hockey League and the Utica Comets of the American Hockey League.
The 28-year-old Coffman has played the last three seasons for Alaska. Last season, Coffman posted 33 points (15g-18a) in 45 games. A native of Elverson, Pa., Coffman has tallied 100 points (40g-60a) in 142 career ECHL games with Alaska and Greenville.
Johnston was acquired last season in a trade with Wichita. Overall in 32 games with Idaho, Wichita and Alaska he picked up 13 points (3g-10a). A native of Calgary, Johnston also has previous ECHL experience with Colorado and Evansville and has 54 points (13g-41a) in 156 career games.