If it wasn't for you needing a locker on front I'd say an old Kawasaki Bayou 400 would be one to look at. It would have enough gears to suit you.

 

Kawasaki had the Prairie 360 up until a year or so ago. Good dependable machine with low range and a way to lock the front end. It uses a small yellow lever on the left handlebar that you hold on to for full lock. Not my favorite system but it does work. It's a shaft driven solid rear axle so it isn't the most comfortable ride.

 

Any Honda Forman 4X4

 

No diff lock.

 

No Diff lock until 2014 and no dedicated low range sub tranny , just a low 1st gear granny gear.

 

Never said go over 30mph. I found on the GF's machine when she had it 1 it was a real PIA to get the machine in super low and diff lock especially if you get stuck with tension on trans. 2 super low and diff lock was way to low of gearing in some cases we just low would have worked way better. With the mod it seemed to help with problem one since you could already be in low and just have to lock up the front end. Made the machine way more user friendly.

 

My father has an old 88 or 90 Suzuki 250 4x4. Has the low and superlow subtrans on it. I'm picking that up within the next while to use as a woods machine. The superlow is crazy low. If the bike could get traction I'm pretty sure you'd haul a house with it.

 

Well, my main goal of getting to the top of the mountain failed. A 6 foot tall ridge to get onto the power line road that crosses the property stopped me. Could not get enough traction to make it over that last super steep foot. Ugh, but started building a ramp and some stairs for that one part that is also super hard to walk up. Going off into pretty steep areas and hooking up huge logs and dragging them out and even up hill was no problem at all. Was extremely impressed with that an old suzuki king quad was capable of, especially in super low with the front locked in. Next trip I will finish my ramp to the power line crossing and then should be able to ride to within 200 feet of the top without any problems, and that is as far as I wanted to take one.

Here is a photo of one of my work horses, and my ramp I started. Having the had rail alone makes it much easier. Trust me a lot steeper then it looks in the picture, yeah with a little momentum and speed someone could easily have gone up it, but at my age that is not for me. Will finish my ramp so I can get up with no problems or risk. Ton of fun dragging logs from where my 2 wheel tractor could not go, then use the tractor to lift the logs into place.