Good luck for trying to figure it out! Can you give an example of an entire expression he might send in an email?
I've never heard it. In my opinion, it's not idiomatic.
I
hope you have good luck trying to figure it out is common.
I wish you good luck for the future is common.
"I wish you good luck for [some purpose]" is certainly grammatically correct. But these are "fixed expressions," and we don't usually just make up new ones, even if they're grammatical.
Well, I just checked Google, and "good luck
for exams" and "good luck
on exams" were about equal, with about 10,000 hits, yours being a little stronger.
Better hope for some more opinions.