I screwed up, I need one #74 Air Bleed

BLP has singles. Not sure what they'd charge to ship one though. 5500 Series Air Bleeds Air Bleeds [5500] - $1.91 : BLP Products

Also, ebay has a 4-pck of them for $12 inc shipping. Or you can buy 10-32 set screws and drill your own (assuming you have a .074 bit, which is a weird size).

I wouldn't think you'd be able to tell any difference between a 73 and 74 air bleed. Good luck.