GAP 4.8.9 installation with standard packages -- copy to your CoCalc project to get it
LoadPackage( "GradedRingForHomalg" ); S := GradedRing( HomalgFieldOfRationalsInDefaultCAS( ) * "a,b,c" );; rand := RandomMatrixBetweenGradedFreeRightModules( [ 1, 2 ], [ 2, 3, 4 ], S );