If you mean between the frame jobs,, ##### carries them. But I would NOT recommend them. They hang way too low for safty. You can go the custom rear-mount route as well. Checl vendors in Custom Classic Trucks magazine.
Try local wrecking yards for the in the cab mounted tanks, or, better yet, move the tank to the rear frame rails using a Blazer, Jeep or other tank that could fit. Getting the tank out of the cab is something I think all truck folks should contimplate.
DV