The challenge with auxiliary tanks for gasoline is that gasoline vehicles have vapor capture systems that are part of the emissions equipment, whereas diesels do not. Any gas auxiliary tank needs to be integrated into the vapor capture system and, for California, must get a CARB exemption. Since these things are expensive, it doesn't make economic sense to produce tanks for anything but the very most high volume applications.
So, that out of the way, you've got a couple of options.
If you live somewhere that doesn't do emissions inspections, you can get a tank for a diesel and use a transfer pump to push from one tank to the other. The one problem with this is that you'll likely wind up with a fault code/check engine light issue.
The other option is to, again, use a diesel tank, but use it as a storage tank only, pulling fuel from it as one would a transfer tank.
There are a number of makers of tanks that fit in the spare tire location, which would work well on the suburban (albeit necessitating relocation of the spare tire itself).
