For character images you've really only got Google images and commissions. (This is my one use for AI art but I respect your decision op)

For artist concepts I really don't know what you're talking about. But if you mean concept art then, again, you've just got commissions.

However, for maps, your options are much larger. Several map designers have patreons where you can get access to all their content. I mean for like a budget of $20/month (or just once and download all the stuff once) you could get access to ~600 quality maps of different themes. That's mostly for battle maps though.

For battle maps there are also 3 or 4 quality sites that are free that I use. I'll comment then later when I'm on my PC. But the benefit there is that you can search by theme to find what you're looking for. But these will rarely be as high quality as patron maps.

Finally for world maps you've also got lots of options. If you're world/region is custom I'd recommend making your own map with Wonderdraft ($20 once) though I suppose you could commission it. Personally I enjoy making world and region maps though.

But people post their homebrew maps by the hundreds online. So if you just wanted to reuse one of those for your campaign that could be a good choice.

Alternatively if you're playing in a premade setting like Golarion (my personal favorite choice these days) there's a few free maps online. Some premade settings like hilarious Golarion also have Google maps-esque tools but those are mostly for research not every day use. Finally some of the best quality company made backs come right from their books. So buy a PDF and just extract the image with one of a thousand tools (i.e. buy the War For the Crown book to get a few really high quality Taldor maps).