Newer cricut user here, so I’m far from an expert but I’ve found https://freesvg.org to have the best free selection of all the sites I’ve tried so far. Source: over 1 year ago

Contextually, what you're doing is fine. You're making personal-use invites for a kid's birthday party so I think it's admirable you're hoping for some casual free resources for use. Generally speaking, you're going to likely be looking for each source on a case-by-case basis because there isn't a single go-to large repository of commercial-quality, diverse free libraries of content. Some get close but they won't... Source: over 1 year ago

Freesvg.org and Vecteezy for illustrations/clip art. The cover of Project BRKN-Shackle uses two versions of the same “spy” graphic, and I then modified it/shifted the colors. I did even less work on Playdate Peril’s cover, just combining a couple illustrations. Source: almost 2 years ago

Not CorelDraw, but I think you can use this site for free SVG's. https://freesvg.org/. Source: almost 2 years ago

What you need is svg files, you can edit them using inkscape, which is free: https://inkscape.org/ There are lots of free public domain svgs here: https://freesvg.org/. Source: about 2 years ago

Stockup - A new library filled with stock Images. Source: almost 2 years ago