I think @DannyW hit the nail on the head: The closest thing to a new AI head will be a used AI head...ideally one that has been treated gently over its lifespan.
Two or three years ago I found myself thinking I needed a backup/spare for my >15-year-old Acoustic Image Focus 1 (Series II) head...and I came up with two possibilities, from completely opposite ends of the spectrum:
- a Walter Woods Electroacoustic Ultra (blue light) ...except A) a WW doesn't sound anything like an AI, and B) Walter Woods is probably not too far behind Rick Jones in terms of time left on this mortal coil, and it'd be even harder to find someone who can repair a Woods once old Walt bites the big one; and
- a tc electronic BQ500 ...which wishes it could grow up to be as nice an amp as an AI, but at least it's 1/3rd the price.
I wound up getting the BQ500. And it doesn't suck, not by any stretch of the imagination. I still prefer the AI, and I pray that there are qualified techs who can service them now that Rick has passed. But the gigs where I've used the BQ500 went just fine, and nobody in the band or audience threw an empty beer bottle at me and yelled "Your tone is poopie, get rid o' that amp now!!" It takes a tiny bit more tweaking of the tone controls to get the tc to replicate the warmth and fullness I get out of the AI, but it's more than passable.
:::shrugs:::