A Rolleiflex or Rolleicord with a set of three Rolleinars is a good alternative. It's not perfect, but it should take care of your close-up desires.
The Rolleinars are of excellent quality.
Horseman VH-R focuses into the macro range without additional equipment, but the rangefinder is only good for about one meter subject distance.
I have it now, it's not a rangefinder, it's a roll film view camera. I have a Galvin which takes a roll film back. That's the lightest camera I have. The 6x9 is a good backup too, no electronics, however, I'll need to bring a meter which is no problem. There is no one camera that does it all.
for 6x6 our Rollei SL66E has a microscope adapter available - if the onboard bellows don't provide enough macro already ... they are a very capable camera
Its not an easy thing. But I used my RB Pro S with extension and a 180mm lens, hand held on this macro. I would use a tripod if I tried it again.
It is not a rangefinder but the Pentax 645 series have some great macro lenses as well as extension tubes, a helical extension tube and even bellows, if that is not enough. I am confused why you want to go with a rangefinder for this type of work?
My Mamiya 645 Pro with the 80mm macro lens focuses very close (36 cm) and gives a half life-size negative or slide.
With the extension tube, it goes down to life-size.
My RB67 with the 140mm macro is similar. It is a lot larger, but the rotating back coupled with a metering chimney finder works really well.
I remembered this thread today.
I'm checking out the 0.7 min. now.
The answer is my GA645zi focused down to 1 meter.