Free vector images from VectorStock - subscriptions are also available:
https://www.vectorstock.com/free-vectors

This site has loads of public domain vectors (hence the name):
https://publicdomainvectors.org/

Freepik has lots of free vectors (.ai or .eps format) and .psd files for download:
https://www.freepik.com/

SewArt - possible alternative embroidery design software (Windows/Mac, has 30-day free trial option, and exports in lots of file types including PES):
https://medium.com/@volkerwandering/how-to-create-an-awesome-embroidery-file-with-sewart-f0ff15d30c5c

The 23 best places to find free vector art online (article):
https://www.creativebloq.com/graphic-design/best-places-free-vector-art-1012985