If you want to buy something face to face about the only place you are likely to find a lucy is at a reptile show. Pet stores generally do not carry anything like that.
I would think your best bet is to go with someone who has a good reputation on the web. You can ask around about who that is with other people and just sit back and watch. You can check the boi. If I buy from someone online, I'd check them out real well prior to the purchase because there most assuredly are scam artists in the Ball Python world. My personal favorite for breeder I know I can trust is Ralph Davis.