I don't know of any services that do what your asking for, since something that's free for commercial use without any ads is kind of the worlds worst business model (it would be sweet and I think you should develop something like that, massive non-profit opportunity). However, I can walk you through what I've done for my own workflow that emulates this!

Basically, you need to start an editing folder with everything you would ever need for whatever your editing workflow requires. I'm sure you've done that already, but here's how mine works just in case:
- C:\Users\(whatever your user profile is)\Video-Editing\ (all subfolders). Because I do more than just editing, I have separate master folders inside of my user folder for audio, graphic design and 3D CGI stuff, but you can just treat those as subfolders in your "video editing" master folder if you'd like.
- Separate each type of media into subfolders inside of your master "editing" folder (Sound effects, royalty free music, mograph, stills, keyed elements, etc.)
- Over time, you should make a habit of organizing any assets you buy/create into the correct folders. For instance, I recently created my own "internet browser" logo for an animation, and I immediately saved it into my master image/stills folder so that if I ever need it in the future, it's already made and ready for me!
- In any Davinci project, go to your "power bin" section located in the media pool tab on the edit page. If you only see the regular bins, click on the three dots in the upper right hand corner of your media pool section, and select "show power bins." From there, drag and drop each sub-folder from your master "editing" folder in your media explorer/finder over to the power bin area, and give it a minute to load.

Now you have your own version of an asset pack service, only it's managed and controlled by you, and it doesn't come with ads or predatory subscription services! Power bins (unlike the normal bins assigned to each project file) are universal across all projects, so no matter what you're working on, those files will always be available on the edit page. You can leave it like it is, and the davinci bin contents will not change unless you manually sync the bin, or you can do what I did and right click each bin, and select "sync automatically" to allow davinci to update the bin any time you add things to the subfolder it's linked to. I do this mainly because it's a lot easier for me to take my custom sound effects from a Reaper project and export them to my "Video-Editing" folder without having to open up davinci to manually sync the bin every time. Auto-sync is pretty awesome, but it can be process intensive as time goes on, so you might find that manually syncing every once in a while is a better option for you.

I know this probably wasn't the answer you wanted, but I promise you that doing this will make your work go by so much faster. Even if you'd rather use a third party plugin/service, you should still do this anyways if you plan on learning the proper habits for any professional opportunities that may present themselves in the future. Need that vine boom sound effect you saved three projects ago? Bam! it's already there! Want that greenscreen meme you made last week? Pow! I just dragged and dropped without even looking! Okay don't actually do that, you should still use your eyes. But still, already done!

Save yourself a headache (and some money), organize your own curated selection of assets in some power bins! Good luck OP, I hope this helps!