Which particular items are you referring to? Engine hard-parts? Drivetrain? I just looked at a few items I normally look at .....didn't see any difference in what I've been seeing lately ....which is, like you say, more items becoming less available. Or unavailable. GM sells their parts stock and if you have anything you really want with a GM sticker on it, you probably ought to buy it now before it's dried up.
Like any short-run vehicle or older car (and non-mainstream classics), parts will become increasingly scarce. That's life. That said, I wouldn't panic too much or start hoarding too much stuff. 1) You never know what's going to fail or not and you can't buy EVERYTHING. 2) A guy can usually find what he needs even it means buying used on ebay or other sources. You could always buy a 'parts truck' too. But yeah, like you pointed out, parts are less available and more expensive. At this point you have to WANT to drive an H3.
I always tell wanna-be gawkers who say: "WOW! ...a H3, they're neat. I've thought about getting one of those!" ...I tell them honestly that unless they have deep pockets, don't mind repairs or hassles, and are really good mechanics, they're better off buying a new Bronco. Most people live check-to-check and are the 'payments-type'. Ongoing repair bills would kill them. And the insurance ain't cheap either ...for such an older rig. Anyway, I'm sure members here are pretty much H3 die-hard's, and the maintenance is either considered theraputic de-stress time, and/or a small price to pay to drive one of the most unique and cool vehicles ever made.