If you can find a nice pair of SIS 6-speed shifters on ebay, go for it. But remember you will also need a compatible band to attach them to downtube of the frame. All of the Tourney models I see on ebay are stem mount shifters and these have a very narrow diameter band. Unfortunately, there were several annoyingly different mounting posts used by Shimano during the late 1970s through late 1980s. So make sure that any separate band you find has the correct style of base and posts to match your shifters.

On the bright side, you do not need to limit your component search to a 6-speed rear derailleur. Any indexing Shimano (or Shimano compatible) rear derailleur - even a far more recent Shimano model should work fine. Even Shimano 9-speed derailleurs will work fine with 6-speed freewheels.

If/when you need a new freewheel, look for a modern "Hyperglide" style. Any new Shimano or even a cheap modern Sunrace or Nashbar model these days should now have those profiled cogs. That's what helps make modern cassettes so extremely accurate to shift through. It was Shimano's greatest breakthrough discovery during the 1980s. Before that every manufacturer had experimented with their own proprietary tooth designs from the chisel shapes of Suntour to the twist-tooth Shimano UG style, and none really worked much better. Hyperglide cogs enable a chain to literally reach across and seat on the next cog before it has completely dropped off the first. The result is smooth and accurate shifts (even in friction mode!).

Really ANY front derailleur and crankset combo should work fine... you're just nudging the chain over a few millimeters. The modern ramps and pins of modern chainrings are excessive engineering for any double chainring crankset on a road bike.