I end up using images.google.com with the query:

<keyword> ext:svg

This usually finds me good options, many from wikimedia etc, which are under a open license.

Many times, if you only can find free and open images, but in raster format, use something like vector magic to convert them to SVG.. VM usually does an excellent job with basic handholding.

Here's an an example search: https://www.google.com/search?q=site:wikimedia.org+ext:svg+-...

Perhaps one of these?

* Openclipart - https://openclipart.org/

* Iconfinder - https://www.iconfinder.com/

From within Inkscape you can use Import Clip Art… from the File menu to search SVG's on https://openclipart.org.

You can use those http://www.freepik.com/ and its sister site http://www.flaticon.com/

For simple objects (that can be a good start for designing stuff around), The Noun Project is great: https://thenounproject.com/