My '88 Schwinn Voyageur was equipped with a 6sp Shimano freewheel on a Maillard hub. 126mm spacing (but a 130mm hub slides in like butter - thank you, long chain stays). It came with 6sp Shimano DT shifters with both index and friction settings.

So, I imagine any 6sp freewheel will fit the bill. I'd just go with an inexpensive SunRace.