Hey Bjoern,
I found this example for you on MotionArray which you can crop to 9:16 format of your choice:
https://motionarray.com/stock-motion-graphics/vertical-filmstrip-overlay-1017168/?q=filmstrip&specs=orientation%3Ahorizontal&subcategories=framing-devices
I’m guessing that you might have two issues in your search:
As there never was, as far as I know, a “vertical” film format, unless possibly for special effects and fairground attractions, this would have to be a custom built in the edit.
And, your search may need to include words like “filmstrip”, which might not be something that you would normally use in film production or the film lab.
Hope that this helps.
Atb
Mads