It's good to have fairly small bottles around to test the carbonation of root beer after a few days. I've been looking for old fashioned 7 oz bottles, but they are very hard to find. Americans are drinking soft drinks in cups as large as 1 quart or 1/2 gallon (1 to 2 liters) nowadays. Just watch the film Only registered users can see links on this board! Get registered or login! to see how portions of everything have increased.

Anyway, I was in a local european grocer/deli and came across bottles of the Dutch chocolate drink called Chocomel. It comes in various sizes, but most importantly in a 20 cL size (6.7 oz).
http://www.popsoda.com/chocomel.html
The bottle has changed shape since this picture and now has a very slim waist. These bottles, that have traditional crown caps, are perfect for home brewing. Chocomel also gets very good reviews online:
http://www.bevnet.com/reviews/chocomel/

Parsa