These are just some standard places that I use that are free to get CAD files from.
https://www.mcmaster.com This one is very good.......
There are loads of others, but I really depends on what you require. I hope this helps you out.............
If it is an existing hole, are you looking @ cosmetic threads? If so you should be using the hole wizard and turn cosmetic threads on.
If you are looking to model some threads, insert>feature>threads will give you the following dialogue box:
The options for the thread are all layed out in here.