There's a few options.
For the GX470 - I'd find an 8.2. They are not a ton larger, but much stronger. Internally - they're a lot more robust. The pinion shaft is much larger and the pinion main bearing is also a lot bigger. The result is a lot less deflection under load and basically no examples of broken parts I know of with factory gear setups. The 8.2 pinion is larger than a Dana 60. (ring gear is obviously smaller).
Here's the two side by side:
Beyond this - Diamond axle builds a Land Cruiser 9.5 center with 4Runner/GX outers. It's a bolt in swap as well.
Or you could make a custom Land Cruiser 9.5 rear end out of a junkyard 9.5. You can buy them with e-lockers, but I'm not sure how they interact electronically with a GX wiring. The main difference is that you'd need to have the rear axles re-drilled for 6 bolt pattern. Since the 6 hole pattern is narrower, I *think*, but haven't done it, that you could simply re-drill without the need to weld in any of the old 5 lug holes. I don't know enough about the linkage mounts - but it's possible that it may even bolt in place or be very close to bolt in with some adjustable links that are not too expensive. The 5 link design is the same. I just don't know about the spacing. I also don't know about ABS tone ring count - if it's the same on both, it'd be very easy to mate the axle to the GX system. Junkyard LC100 rear axles go for around $500-800 that I've seen.
Next option is the Tacoma 8.7. It's actually 8.9" ring gear. It's probably stronger than any of the older OEM Dana 60 axles because of the larger stronger pinion and pinion support bearing. They're pretty cheap. But they have drum brakes...
If you wanted to get something shipped - the fortuner has the 8.9" ring gear rear axle just like the Tacoma, but is already setup for 5 link and comes with disk brakes. It's probably a bolt in swap. And it also has an internal e-locker option. The downside is that finding one in the USA will not be common and shipping probably isn't cheap.
Tundra rear axles are BEEF, but they're heavy and probably overkill for a GX. They are pretty reasonable cost wise and pretty widely available. Like the junkyard 9.5LC, you'd have to re-drill the rear for the 6 hole pattern. And they're pretty wide for a GX. I'm sure you could get a custom housing or narrow one, but you'd be spending a lot to do it.
After that - you're probably going into more complicated non-toyota options or aftermarket axles. There's maybe a handfull of bolt in options or junkyard axles plus weld on bracket kits.
Biggest thing I'd avoid is a Dana 44. They're almost all or all going to be weaker than an 8.2 that is a very easy and economical swap. So - Dana 60 or bigger if you want any strength benefit.
If you want to fab your own - Ford 9" build kits are pretty cost effective. Biggest downside is that 9" rear axles kinda suck as far as pinion location. It's very low in the housing so your drive shaft will be a rock magnet.