PEM for VM/CMS

Is the a PEM system for VM/CMS yet?  I guess the more general question would
be what PEM implementations are available?  Our computer center is running
an X.500 directory server and I assume that storing public keys in such a
beast would be a reasonable thing to do.  All we would then need is the
mail systems to be able to make use of it.

So, is there a list of available PEM implentations somewhere?

Thanks,
Dan Ehrlich