Mixers (Dances)?
Find out what style of dancing is typically danced at those mixers and take some classes in that style. I'm sure you can find something in your local dance studios or maybe some evening classes in community colleges - usually you don't have to enroll...
What is the shelf life of Bar Mixers like Marguarita mix or cosmopolitan Mix?
All mixers should have an expiration date on the label somewhere. I would think they should be good for a few months at least from date of purchase. If there is no date, follow the old rule: when in doubt, throw it out. Better to be safe than sorry
How many concrete mixers are there in the U.S.?
It is probably in the millions of blades sold. Here are the websites of people in that business and most hold patents for their blades. Product liability would be a factor as well.