Well, this site (i.e. PerlMonks) is full of Perl puzzles. There's new troubleshooting puzzles in Seekers of Perl Wisdom every day. For really advanced puzzles, try determining how any code posted to Obfuscation works.

Nearly every Perl book I've ever read has had multiple instances of: "XXX is left as an exercise to the reader". While I'm happy to be corrected, I suspect O'Reilly has the largest collection of Perl books. I wasn't intending to post any particular title but, when checking the URL for O'Reilly, I did notice Games, Diversions & Perl Culture which is possibly the type of thing you're looking for. A general Internet search may be better but be prepared for a large result set unless you're specific: googling just 'perl book' indicated over 6 million results.