Here's the story I heard a while ago : apparently, the machinery that was used in the 70-80's to make the original 'ensolite' was fairly complex and the manufacturing process was pretty tedious (by today's standards), even though they made a lot of it back then. The machine was very likely put out of commission a long time ago, or perhaps even destroyed, as very few people knew (or cared about) how to operate it due to the cost.
I'm not sure why nobody else has figured out how to make similar stuff in the following years, as from what I understand, nothing comes close to it (even today) in terms of stretchability and manoeuvrability, especially in and around corners. But your best bet might be to contact one of the FG manufacturers and ask them what they use today.
Driving on parkways and parking in driveways.