The smallest size is about an 18. Most shops won't carry a barbell in that gauge so you would have to special order it. Talk to your piercer and see what they have to say.

you generally dont want to go smaller than a 14 because that's pretty much the industry standard and if you go much smaller than a 16 it's going to be nearly impossible to find jewlery to fit it. yes the holes will close completely if you decide to retire the piercing later

My best friend just got hers done about a month ago and hers bled like crazy. I'm not trying to talk you out of it just be prepared to have dark pillowcases because for about a week her ear would bleed. But she loves it now.

18 gauge is the smallest i've seen