Are there any statistics available about the rate of divorce for
students while they are in grad school - both master's and doctoral
grad programs?  I already have statistics for people at various
education levels after they have completed their education, but not
while they are actually involved in their education.

For researchers attempting working on this question, this previous
answer, which has the statistics Stodes mentioned on people after they
have completed their education, might be helpful:

https://answers.google.com/answers/main?cmd=threadview&id=149727