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