Can the "G" and "VRB" wind conditions be combined in METARs? I have never seen the "VRB" (for wind direction variations &lt; 60°; e.g. VRB12003KT) and "G" annotation (for gusts > 10KT wind speed difference; e.g. 12003GT30KT) being combined in a METAR.

Until now I have just seen: 


VRB03KT (so "VRB" without gusts)  
12003G30KT 090V150 (so "G" with wind direction variation > 60°)


Why does this never happen? Is there a rule and is it not possible or does it just never happen?
Yes, it is possible for a METAR to contain both VRB and G. VRB10G25KT is valid.

The reason it rarely happens is because, as wind speed increases, major variations in wind directions tend to disappear.