I found a couple of awesome resources for PowerBi icons that you can use in diagrams.
1. Official repo of PBI icons: microsoft/PowerBI-Icons: Icons (PNG and SVG) for Power BI (github.com)
2. Marc Lelijveld repo: Marc has provided an xml document that allows you to easily import all the icons into Draw.Io. This makes the whole process extremely easy. marclelijveld/Power-BI-Icons: Icons (PNG and SVG) for Power BI (github.com). The most import link from Marc's repo is the raw link to the xml file: https://raw.githubusercontent.com/marclelijveld/Power-BI-Icons/main/Diagrams.net_PowerBIIcons.xml. This link can be used in Draw.Io via File >>Open Library from >> URL...
Once done, you will get all the icons in the left pane:
Here is more info from Marc's blog: Power BI Icon Library – now includes official icons to use in Draw.io / Diagrams.net – Data – Marc (data-marc.com)