[R] Modified Bessel Function - 2nd kind

[Dr Andrew Wilson]

In order to fit a probability distribution proposed by Sichel [Journal of
the Royal Statistical Society. Series A (General), Vol. 137, 
No. 1. (1974), pp. 25-34], I need a modified Bessel function of the 2nd
kind.  I notice that the base package of "R" only has modified Bessel
functions of the 1st and 3rd kind.  Does a modified Bessel function of the
2nd kind exist anywhere?

Many thanks,
Andrew Wilson