I have LT315/75R16 tires on my truck. It's a 99 GMC Sierra 1500. Where can I...

[Barky]

...find some 40" mud tires for it? I've been lookin all over
And all these different numbers and everything get confusing
Im even willing to switch rims
I just want mud/swamper tires between 39"-41"
Any help is greatly appreciated