I had to get it in quarts myself from advanced auto parts. They had the $24.99 or $29 (can't remember) for 5 quarts and a free bosch filter special going last month. I got an extra filter for my other cars as I only use napa gold for my Porsche.
You could always have them order it in from another store. I don't think they even charge for it. Good call on castro syntec!! Don't forget to check your old filter for metal particles