Ford has em pretty cheap for a bag of 16. NAPA does have the O-rings in a rebuild kit for the injectors. I JUST bought them ... from BOTH places! I can get the NAPA part number if ya need it. RIO50 told me about them!!
It includes the plastic tip, the spacer, and the two o-rings. Maybe the O-rings are available seperately - I dont know about NAPA, but like i said, they are available from Ford.