I'd recommend a trackball, there are very few mice that are comfortable for large hands, especially palm grip mice. You'd think there would be more larger palm mice, but no.
As for regular mice:
The RAT7 can be adjusted, although I'm not sure if it can be made all that large, but it's worth considering at least. The Razer Lachesis is also a mouse that I've heard good things about from people with large hands, but that's EOL so you'll have to find a used one somewhere. It's not palm grip though.
The Func MS-3 is fairly large and suited for palm grip, but again it's not all that much bigger than most other mice.
I really would recommend a trackball, something like the CST LTrac(currently on Massdrop for $99, 2 days left) or Kensington Slimblade.
I'm also a fan of tablets, and can also recommend a small one if you've got the space for it on your desk, but it does take up more space compared to a trackball, so unless you'd like to be able to draw or write handwritten notes on your PC I'd still recommend a trackball over a tablet.