I am having a hard time finding out how many United Statesians 
are killed in weight lifting accidents each year. Any ideas on where to look?
This is just my wild-asss guess, but have you tried the Center for Disease Control? They usually have statistics like that.
The book that would list this sort of stuff is called “Injury Facts”. You should be able to find it a library. It used to be called “Accident Facts.”
It’s published by the National Safety Council. I don’t know if weightlifting accidents are separated out however. They may just fall under “exercise”.
The book is very specific about things like falls and automobile accidents.
I actually was able to track down a copy of “Injury Facts.” Unfortunately for the OP, there is no figure for weightlifting fatalities. There was a figure for 1997 for injuries from “Exercise with equipment”. That total was 86,024 (if I copied the numbers correctly.) This does include weightlifting, but it also includes people falling off treadmills and other such stuff. The National Sporting Goods Council did this survey.
There might be a study in some medical literature, but I doubt it would be a nationwide study.