Perhaps you already know this but DNA palindrome is a fairly casual way of saying inverted repeat. Not trying to be picky but the latter term should help with the search.

With this in mind, BioPerl has an interface to the relevant function of the popular (and huge) EMBOSS package.

Possibly a bit too narrow but you might also want to take a look at a recent paper which uses a Perl script to find a particular type of inverted repeat (MITE).