I have come across this problem once before, and in doing some research, I could only find an approximated standard error for each. For the skewness:
SES = sqrt(6/n)
where n is the sample size. As a general rule, this approximation is best when n > 150. For the kurtosis:
SEK = sqrt(24/n)
and the general rule here is n > 1000
Hope this helps.
~Matt