As best I can tell, there are about five different brands of 00 flour available in the U.S. at the retail level: Bel Aria, Delverde, Caputo, the KA 00 clone (which is really a domestic flour), and Pelegrino. I have tried all but the Pelegrino brand (which is available at isolaimports.com). I had problems using the Delverde and KA 00 flours in my recipes for Neapolitan style doughs, but good success using the Bel Aria brand. I haven't had much experience to date with the Caputo flour, which I received just recently, but it also looks to be a good product for my uses. The Caputo product is widely used by professional pizza operators in Italy and, to a lesser degree, in the U.S. The advantage that the Caputo product has over the Bel Aria product is that the Caputo 00 has a higher protein content (11.5-12.5%) than the Bel Aria 00 (which I am told is around 10%) and provides greater crust browning than a crust made with the Bel Aria 00 (although I have overcome this difference somewhat by using sugar and oil in the Bel Aria dough and oil on the shaped dough round).
The Bel Aria 00 flour is sold by the bag (1 kilo) in some retail shops, particularly in Italian neighborhoods, and also by Fresh Direct (at $1.49 a bag) if you happen to live in Fresh Direct's zip code service areas in NYC. The Bel Aria 00 is also sold by the bag ($1.99) by PennMac (at pennmac.com), and also in a ten-pack unit at a discounted per unit price if you call PennMac (1-800-223-5928; 412-471-5928) and ask for Rose and tell her you are a member of this forum. The Bel Aria ten-pack is also available from chefswarehouse.com, but only in the ten-pack case, for $12.42. Shipping costs also have to be considered so you should compare total price with shipping costs added to determine which offers the better deal. If you are not sure whether you will like the 00 flour and the pizza doughs it makes, you might want to try ordering a bag or two to test to see if it meets your needs. If you are also interested in other pizza-related products, such as San Marzano tomatoes and cheeses, PennMac offers a wide variety of such products that you might want to consider along with buying a few bags of the Bel Aria flour, if that's the way you choose to go. Remember also that PennMac sells many more products than shown at its website, so you may want to speak with Rose about specific product needs.
The Caputo 00 "pizza" flour is available at both PennMac and chefswarehouse, but only in a 25 kilo bag (55 lbs.). Fellow member jftaylor recently purchase a bag from PennMac at a good price (I believe it was better than chefswarehouse's price of $72.40, including shipping) by speaking directly with Rose. I have spoken personally with the NY-area importer of the Caputo 00 flour to see if there are smaller 1-kilo bags sold anywhere in the U.S. at the retail level and was recently given a possible lead, but haven't yet had a chance to follow up on the lead. Again, it would be nice to try out a small bag before committing to a 55-lb bag.