There are a lot of replacement parts available. But a lot no longer are. They never had the aftermarket support Toyota FJ's had ..or Jeeps. Not even close. I've had a lot of people say, "Wow, a hummer, I'd like to get one of those!", and I caution them that they can be expensive vehicles to own. Esp if a person relies on a shop to do repairs. Definitely not for the faint of wallet. There's one in our town and I see it up at the local repair shop all the time. It's only a matter of time before the owner gets tired of putting $$ into it.
I've had to go through and replace more things on my H3 than any other vehicle I own. Part of that was deferred maintenance from the PO (due to cost of ownership I'm sure). But it's been very reliable for the last couple years after I went through things. Now at 190k, I'm getting ready to yank the engine and re-do that (repl engines no longer avail). But I love it and I'm in it for the long haul. To me it's a labor of love. That's how you have to look at it. For owners who get figitey from spending x, y & z money on repairs and look at it like an investment, it'll be a killer. A new Bronco might offer more peace of mind.
If you can do your own maintenance, most or all of the common failure items are available. A few items might need to come from ebay (used) every once in a while. For the most part, I haven't had problems finding parts. But aftermarket items are more rare. And BTW, not a whole lot of these are related to the Colorado. I think it was 15% and most of that was from the firewall forward.