Stem Mounted Shimano 5 Speed Index Levers - # SL-S452-5 (also came -6 & -7 indexed)
Bar Mounted Indexed Thumb Shifters - #SL-MS52 (also came -6 & -7 indexed) and # SL-TY15 (Tourney)
Shimano also made a 4 spd indexed thumb shifter.
These 3 above are all plastic except for the clamp band (steel) but will work with the current 5 sp Shimano, Falcon and Sunrace freewheels which seem to only come in 14-28 cogs.
My info may be out of date since I'm working from a Shimano '93 parts catalog and a 2003 QBP catalog.
I had a set of the Tourney 5 spd shifters salvaged from a Murray MTB my neighbor pitched and they actually worked but you really need to like plastic and indexed front shifting (at least on this pair).