You can search for the following on iTunes:
No Challenges Remaining
This podcast features SI Tennis blogger Courtney Nguyen (Beyond the Baseline) and New York Times contributor Ben Rothenberg. This is one of my favorite podcasts and they try to broadcast at least once per week.
Tennis Magazine has a good podcast with Steve Tignor, Pete Bodo, and Ed McGrogan. They try to broadcast every couple of weeks and more often during the Slams.
Tennis Podcast with Jon Wertheim
Jon Wertheim of Sports Illustrated interviews current and former players. This podcast is less frequent, but always interesting.