The remote control that I got was the Liftmaster 81LM, it is cheap and works fine with this opener.

Product Description

This Liftmaster 81LM is equivalent to the 139 model number. It is compatible with operators manufactured between 1993-1997 and uses a "Smart" coding button with a Green LED light that will light up when you press the smart button on the back of the overhead motor to program the remote. The 81LM is a 2 channel transmitter, compatible with the "Billion Code" series. It includes a visor clip and Lithium battery (5 years life with normal use), also instructions come with the remote. The wireless keypad that is compatible with this Sears Craftsman garage door opener is the 66LM (Chamberlain 850CB, 853CB, 856CB).

or the Sears

Sears Craftsman 139.53628SRT Remote