RPM makes a set of StableMaxx rims that have a 1/2 inch offset.
ProLine also makes a set of offset rims with the same amount of offset. The 40 series rims are just plain wide. Not certain that they actually add much in the way of offset, but they do run more stable.
IMEX also makes a JumboMaxx series of rims and tires that are pretty wide (no offset really, just wide).