Are there aftermarket small form factor 4k cameras?

Hi all, I hope this is the proper place to ask this. I have an old DIY drone that I purchased a few years ago. I bought it used already built with DJI parts and radio, but no camera and would love to retrofit it with the PX4 ecosystem.

I wanted to know if there are aftermarket small sized 4K cameras like you see on Yuneec and DJI drones. I’ve searched the internet but have come up short on anything.

Or, can a Yuneec or DJI camera be purchased and mounted onto a DIY drone with the PX4 ecosystem?

Thanks for any feedback, greatly appreciated.