There was a scene in episode # 2 of the Macross Plus OVA, where both the YF-19 in fighter mode and YF-21 in fighter mode can be seen firing their twin forward firing beam guns (wing root guns in the case of the YF-19 and elbow guns in the case of the YF-21).
And in Macross 7, there are many scenes where the VF-17D/S fighters and battroids fire their twin beam guns on the side of the cockpit/chest, although most of the time you have to be watching in slow motion to catch it.
I think in the first Macross Frontier preview clip, the VF-171 can also be shown firing the cockpit guns.
Graham