Does anyway know a safe reliable sight to do buy the paris museum pass before I go?
No one here (99.9%) buys the pass before they go.
...because it is cheaper in Paris and easy, too!
I'm the 1% who bought the pass online from this site:
http://www.parismuseumpass.com/en/home.php
It was reliable and quick--no problem whatsoever. I probably did spend more with postage and whatnot but it is nice to have it before I get to Paris. To save money, you might just want to get it there.
The pass is the same price but the shipping which takes up to 10 days is €13.50. (When purchasing for 8 of us in 2005, 13.50 divided by 8 isn't too bad!)