The part that you are looking for is called a headliner retainer side valance. To my knowledge, these are not available in the after market.
A retainer can be fashioned with some effort, they are not that hard to make.

You are the "go to man" Fred! I knew it had a specific name which now I should be able to track down. Thanks very much Fred!

Ply-grip. Comes on a roll and bendable around corners. Either pop rivet it on or staples.

Thanks Jack!

Despite I used it in the seventies I never knew the correct name in English. I am also curious to update names of some upholstery materials.
After several comments, I have realized we are clearly talking about 'headliner retaining strips':https://www.ebay.com/itm/52-53-54-FORD-MERCURY-SET-ROOF-TOP-HEADLINER-RETAINER-RETAINING-TACK-STRIPS-TRIM-/131181235492?nma=true&si=HV5UHkAvCcJyziiBlo5Ecd6UnGw%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557
In the worst case scenario, of not getting the original we would use the 'Ply grip flex trim':
https://www.ebay.com.au/itm/Professional-Flexible-Metal-Back-Tacking-Strip-Ply-Grip-1-5-Metre-Lengths-/141968515741

Ply-grip is used mainly in furniture upholstery for blind edging backs. Is has been used in the automotive industry to fill the need of lost or missing parts. When used correctly, ply-grip yields excellent results.

Use a piece of 5 mm luan. Hold it in place before the headliner goes in and carefully trace it, cut it and sand a slight bevel in the side that goes against the car. Drill several holes to screw it into place and test fit. When you are ready to install the headliner give your beveled edge a good coat of hhr glue and screw it into place (after it has dried enough to not stick to the windlace). Then give your headliner a light coat of glue when you're ready to tuck the headliner. It gives a much cleaner edge than plygrip. I do this for all of my headliners unless the retainers are in excellent shape.

any pics ??

Another alternative is to use the plastic snap edge. The profile of the plastic mimics the metal retainer. I used a heat gun to shape it and then rivet it in place. Brush glue along the lower edge and tuck your headliner material under. It worked well on this custom suspended headliner I did for an Econoline pick up.

Thanks for all the tips! Shoebox central in OK has originals so went with them.

Just to follow up. The J-Clip is part # SC-008. I get them from Pyramid Trim Products. In St. Paul, Minnesota.

Thanks for the shout out Fred! We really appreciate it!