Atlas is a standard in the off-road world. TWF is another: http://www.trailworthyfab.com/Hero-Transfer-Case/

I know they’ve built some transfer cases for custom applications such as 6x6 and such. They could likely build something for your requirements.

The other thing to consider is a high pinion front axle so that you’re operating on the drive side of the gears. A low pinion axle in the front is operating on the coast side of the gears - similar to a low pinion rear axle operating in reverse. The downside is that the high pinion axle will likely create some driveline clearance issues over a low pinion axle.