The national sponsoring organization for weightlifting is USA Weightlifting. Masters Weightlifting is a committee of USA Weightlifting which operates its own website and will host the 2017 Masters Weightlifting Nationals in Savanah, GA
For those interested in Masters weightlifting, I recommend a new book by Matt Foreman, Olympic Weightlifting for Masters. It is full of good advice, interviews with some very successful weightlifters, and some detailed suggestions for training. It's published by Catalyst Athletics and available on Amazon.
Here is the contact information for USA Weightlifting and the website addresses for USA Weightlifting and Masters Weightlifting.
1 Olympic Plaza
Colorado Springs, Colorado 80909
Phone: (719) 866-4508