Palmolive Bath Bar soap is here at my HEB in DFW TX! It come in that 1970's retro packaging.
Next on your list should be Ivory soap. It used to be advertised as a shave soap.
I can get the Palmolive soap from Family Dollar, and Dollar Tree here in Michigan, so I wouldn't say it's exactly rare. Pretty sure I have seen it at Big Lots too. It normally goes for the bargain price of 3 bars for $1.
It's a pretty good bath soap, but has a rather unique scent. I would much rather use Yardley at $1 per bar, as the scents are way better.