"...IMI was loading it..." Yep, but not for a very long time. They were asked about it, a few years back(discussed, at length, on their web forum) and they said they'd do another run if somebody ordered a million rounds and paid up front. Otherwise, go away and stop bothering us. We're busy with military orders.
"...For bullets..." Jacketed bullets are relatively easy. Cast are impossible unless you make 'em. Most .41 Mag cast are SWC's. The AE doesn't feed 'em well.
"....41AE proof ammo..." Very high priced collector grade stuff.
"...haven't seen much .41AE shooting ammo in the States..." Not made by anybody. The .40 S&W killed it.