We found this item: https://www.d20pfsrd.com/magic-items/wondrous-items/a-b/banner-lord-s/
I thought for some reason to remember this was a cavalier specific item, yet it says nowhere that this is the case. Am I misremembering? Thanks!
Yes, banners are ordinary magic items, that can be used by anyone. Some banners have special requirements to use (e.g. Champion's Banner, Commander's Banner) or grant additional abilities upon meeting certain prerequisites (e.g. Banner of the Ancient Kings), but unless a banner specifically states such a requirement, you are free to use them with any character.
You can find more Banners here.