I know that SOME hot keepers do stock antivenin for the exotic species they keep. However, I'm not in contact with any of them currently, so I can't just ask them where they get it or what procedure they use for shelf life.
I do know that Cro-fab(rattlesnake antivenin) can take several vials to treat a bite, so it can get pricy in a hurry. If the antivenin has a shelf life, you'd be buying very pricy stuff that you might need to toss out unused(hopefully!) and buy all new again every year or however long.
The venom lab down south of me produces venom, but I don't think they produce the actual antivenin themselves. You could contact them and explain what you need to know and see what advice they could give you. They seemed like super nice folks when I was there.
http://www.medtoxin.com/
As far as someone saying it's bad juju to buy antivenin, that's ridiculous. You're planning for if the worst happens. It's like saying you shouldn't wear your seatbelt because it might cause you to have an accident. I would consider it to be a responsible thing to do, since if you've gotten your antivenin available WHEN/IF you do get a bite, you're not putting the local hospitals in the position of trying to find the right antivenin on short notice.
However, you might check with the local hospitals too, to make certain they can/will administer antivenin that they did not bring in themselves. They might not be able to give you 'outside meds' because of liability.
I applaud you for doing your fact-checking and pre-planning BEFORE you have a hot and before you have an issue of any sort. Whether you end up with hots, decide to have antivenin on hand, etc, it's never bad to research ahead of time.