The exponential generating function for permutations of order dividing $k$ is 
$$\exp\biggl(\sum_{d\mid k} \frac{x^d}{d}\biggr).$$ These are permutations in which every cycle length divides $k$. You can find the exponential generating function for permutations of order $k$ from this by M\"obius inversion; there won't be a simpler formula.