Has anyone tried reaching out to CBI to see if they'd do another run of rears?
As someone who makes aftermarket car parts I
very highly doubt it. Usually when things are taken off the catalog it's for good, but you can reach out and ask anyways, they're pretty responsive. If I had to take a guess I would assume the major rise in the price of steel along with general strain of the pandemic forced them to remove less popular items and thin out their inventory. Materials, production and storage are the three of the four biggest costs to manufacturing after all.
I was one of the very last to buy their hybrid rear bumper, or at least I suspect so; within a week or two of my purchase the price increased $500, another week or two after that it was removed completely. Mine also took like 1/3 of the time I was quoted and had a good bit of surface rust all over when it arrived, very akin to something sitting around for a number of months in a humid machine shop; giving the impression they already had one laying around going unsold.
What double sucks is they also removed all the accessories that go for these bumpers too, which really gives the impression they're committed to the product cancellation, but you never know I guess - I'm gonna take a stab and say these bumpers required a good bit of investment with custom welding jigs, all sorts of fixtures for it's respective pieces, etc. and would be very strange for someone to just up and throw away that money unless it was for a very good reason.
With all that said, you can still find some vendors offering them for sale if you just google "CBI hybrid bumper 96-02 4Runner." It appears
Vivid Racing,
Morris 4x4 Center, and
Overlander.com all offer it, albeit with varying options; either plain bumper for 2" of body lift, single swingout with angled tire carrier (no BL), or double swingout with vertical tire carrier (no BL). All very appropriately priced - very close to what CBI sold them for.