Sourdough starter?

I make all our bread from scratch - regular loaves, rolls, buns, pitas, tortillas, dough, etc.

I really want to try sourdough, but I have no idea where to get it. I have two friends with starters, but they live across the country. Do I just go to a bakery and buy it? It feels like a secret society lol.

Please help with my entrance into the secret sourdough society!