There are really two effective ways to make a main hand, off hand switching macro. I'll type out all of the commands u'll need to know.
Method #1 if your off hand is classified as an off hand instead of a one hand you may use this simple macro. Hold alt to switch back to your other set.
/equip Item
/equip 2Item
/equip [modifier:alt]Item
/equip [modifier:alt]2Item
*replace item with the weapon name.
Method #2 Equip your weapons directly to a slot if you have 1 handers. Hold alt to switch back to your other set. this uses slots 16 = main hand, 17 = offhand.
/equipslot 16 Item
/equipslot 17 Item2
/equipslot 16 [modifier:alt]Item
/equipslot 17 [modifier:alt]2Item