WTB: NA Beltline Molding (Rubber on door)
 

It's the outside rubber piece on the door that meets the window.

Anyone have one in good shape?

If you can't find one used that you want, Planet Miata has an aftermarket version available:

Planet-Miata.com - Your #1 source for Mazda Miata new and used parts and accessories.

If I were going to guess, I'd say it's probably the I.L. Motorsport version.

Miata Right Beltline Molding LEFT (DRIVER SIDE)

Very difficult to find nice ones used. I looked for a while. I ended up springing for new at Rosenthal. It was about $150 for the pair. Even if you can it's pretty difficult to get them off without breaking 20 year old clips.

W/STRIP RT (NA01-58-810F) - $73.43 - NA0158810F
W/STRIP LT (NA01-59-810F) - $79.25 - NA0159810F

EIDT: Looks like the ILM parts are quite a bit cheaper than OEM.