Bluepant, thanks, that is a great source (they carry an amazing range of felts and other auto related material)! Also, keying on 'bitumen', a few potential sources show up in the UK, so there are some options, as you suggest.
Wanted to add 2 photos of what may be an OEM 'top mat' for the passenger side. It's about 2" shorter than the carpet section that it lays on, but otherwise matches (i.e., same material, same vinyl binding). Unlike the driver's side mat it does not have a rubber 'heel-protector' section.
It is affixed by 6 small Velcro pads that are sewn to the carpet.....so there must be 6 velco tabs on the carpet below??! Or did it just lay there, Velcro doing nothing (it DOES fit tightly in the foot well). Does anyone think this is original?