Ima2many: I saw the study, and it is flawed. He gets his 613 number on a weighted average of his sample size. However, almost 73% of his pomegranates were from the US! You need to represent the actual distribution of pomegranates in the sample size in order to get a real estimate.
As for a source, I’ve heard the Malbim says a pomegranate has 613 seeds.