They are no longer made. Period.

There are double sided monstrosities from one manufacturer (forgot their name right now). Expensive and with solder eyes instead of crimp contacts - but is an alternative for a few of the sizes.

Normally they can not be cut to length. The internal keying is different between the sizes which prevents this in most cases.
And in all their wisdom, Molex discontinued this connector size which still had a decent user base (arcade/pinball machines is not the only place these are used) and replaced them with a new series which has all new keying and are incompatible. This new series had no existing customer base so nobody knows why they did this, not even the Molex sales when I asked them.

You could but the connector seems to loose structural integrity when you do this - depending on size and key locations.

I absolutely agree that new options should be added for edge connector usage on all gottlieb boards.
Some are considered doing this to a slight degree by starting to add ribbon cable interconnect option between sys 80 MPU and driver boards. But so far there is no standard in the interconnect pinouts. I think we need to define a standard one of these days.
I do find it strange that Ni-Wumpf offers driver boards with ribbon cable headers but no corresponding ribbon cables on their MPU boards. And there is this note on their sys 80 page - "Please note that the 50-pin IDC connector at the top of the board is no longer supplied as shown in the picture above"

The single sided edge connectors would be easy -- match the edge connector to a 0.156" header pin for pin.