Pretty much all the functional models I use are free. I get them from www.printables.com makerworld.com www.thingiverse.com thangs.com or I design them myself. Back when I was on Mac I would use Fusion but lately I’ve been 100% Linux so I’ve been using FreeCAD and it’s way better since v1.0.

As far as paid models, it’s mostly been things from www.myminifactory.com and generally sculpts because I want to support authors. Sometimes it’s through patreon but they usually send myminifactory links to redeem.

But yeah, get yourself a pair of calipers and learn a CAD program.