How are gears and mechanisms designed for hobbyist-level projects?

For context, I'm a freshman mechanical engineering student, and I have some experience with SolidWorks and Arduino, and a single project under my belt. I've been wanting to delve deeper into implementing gears and some mechanisms into my build (rack and pinion, planetary gears, and make stuff of the sort).

To summarize my question in a sentence: Do people design the gears and pinions themselves, or can they find a ready-to-use version somewhere?

I've looked at the design library's toolbox, and it has enough customization for spur gears and other pieces. But I haven't found anything else like a worm-gear or a cam mechanism. Is there anywhere I can get those? Or do people usually design that themselves? I would really appreciate a bit of guidance from someone more experienced.