Isuzu still has a few parts distribution warehouses across the country, so it's not too bad. Plus it's not like they've pulled completely out of North America - they still have a viable medium/heavy duty truck business here, so I imagine continuing to provide mechanical parts isn't that big an issue for them.

For the most part your major mechanical parts (engine, drivetrain, etc.) are relatively easy to find/order, especially since many of them are shared with the Trooper. Where you run into problems is with body panels, exterior/interior trim pieces, and accessories. Even so, you can usually find even the rarest of items (roof rail covers for example) on eBay if you're patient enough. Plus folks here are very helpful - usually posting a WTB thread will get you plenty of responses.

So no major worries, at least not yet. Welcome to the obsession!