Finding them is easy. Just type fonts+mac into the Google search bar. As far as safety, fonts have not been know to cary any kind of malware. The downside is that you'll find tons of free fonts, and the majority of free fonts are garbage.
Good fonts cost money, and they aren't cheap. At least not from Adobe, Linotype and some others. There are some free fonts out there that are well made, but they are few and far between.
There are some good fonts here that are pretty cheap.
http://www.macwareinc.com/fontpacks.html
I have all the sets, and sets 3 and 4 are nicely made OpenType fonts. Set two is in TrueType format. Set one is the oddball, consisting almost all of free fonts they collected and sold on disk. They also have FontPack Pro.
http://www.macwareinc.com/products/FontLibrary/overview.html
This is another set of 1000 unique fonts. Also pretty nicely made.
You can sometimes find these packages grouped together for even less at Amazon.