I didn't find barnicles at the pet store (well, except for plastic ones).
You have to go to a craft store! I found beautiful, natural sea shells and purple barnicles at Michael's craft store. They are already sanitized (although I still washed them in hot water and let them sit in water treatment mix for over an hour). The bonus being they were cheaper than any at the pet stores and they were already safe to use because the companies had to make them so before selling them to humans.
The down side is that natural barnicles (or at least the ones I saw) were pink and purple...not very masculine and kind of big and ugly looking. LOL