Ebay if you want an actual antique. But several hatchery sells them in their catalogs. Meyerhatchery.com is one that I just recently came across. They offer both the 15 dozen and 7 dozen size at $23.87 and 17.25 respectively.
I buy them where I find them. I've found them at Habitat for Humanity stores, fleamarkets, ebay...junk stores...etc. I kind of collect them and if I come across one, I simply can't resist.
Me, I had rather have one of the ash woven ones like my grandmother had. I make them occasionally and love mine. It brings back so many good memories of her. The one I use is small but have several of them I have made that are larger and decorate with them. I even made two for my granddaughters to carry as flower girls at my wedding.