There are 4 basic tracks to accomplishing what you want.
1) Buy some decent equipment, used or new, watch some videos and read some books then spend your time practicing.
Advantage: you work at your own pace in your own time frame.
Disadvantage: Slow and ponderous because there is no one to correct your errors and offer assistance.
2) Try offering free labor to one of your local 'smiths evenings and weekends. Not all of your spare time but enough to make you somewhat valuable to the 'smith. Even if you spend the time cleaning firearms or media blasting parts, you will be in the environment watching, asking questions while making yourself more valuable by learning.
3) The NRA or other short courses in which you can learn a lot in a short period of time. Be sure to have some of the tools and equipment available after the classes so you can practice what you learned.
4) Local community colleges that offer machining programs.
North Idaho College:
https://www.nic.edu/programs/viewprogram.aspx?program_id=43
You do not have to be a full time student so scheduling can be flexible. Be interested in a program but take the courses you want but in the order they suggest. These programs are developed with the understanding that not everyone will be a full time student and that there are folks who want to enhance there knowledge base without the need of a degree.
Kick it around, think it over and see if any of this fits you. Then you can always ask more questions.
Enjoy the process!