Actually I managed to find a similar icon in vectorial format, which I could easily colorise. My sidebar with some databases now looks like this:
If any one wants to download the icons I made, the download link is: http://pc.cd/dq9
Here is a preview of them:
Apple has an official page that explains how to change the icon of files and folders via Finder and using the Get Info: https://support.apple.com/guide/mac-help/create-custom-icons-files-folders-mac-mchlp2313/mac.