The main characters are Clint Barton and Phil Coulson. One of them is a vampire already (I think it's Clint, but it may be Phil), the other is not. The non-vampire is severely injured, the vampire turns him to save his life, then takes him to a secluded place for the new vampire to finish the vampiring process. The turning was not something that was pre-planned.
All I remember was the already-vampire making a stop at a Vampire Blood Bank (possibly a Vampire Bar) for "supplies" for the new vampire. He was given priority service because he "has a fledgling out in the car".
I'm assuming that this takes place just after the Battle of New York, and that it's Clint saving Loki-stabbed Phil's life by turning him into a vampire. It's not a new fic - I read it a year or two ago.
Thanks in advance. :)