Hi, it's a tough (aviation) world so just keep trying. I can imagine it's hard.
The only thing I can help you with is the two wiki pages with a list of operators:
http://en.wikipedia.org/wiki/ATR_42
http://en.wikipedia.org/wiki/ATR_72
I have looked at the website of atraircraft too but couldc't find a customers list, so maybe you know where to find it, you could get a very complete customer list and check that as well.
Thats how I've sent every A320 user in the world a letter.
Keep it going and good luck.