I’m assuming you’re talking about the AX short action chassis, not the AXMC magnum long action chassis. Yes, an AT action will fit in an AX chassis; the actions themselves are identical.
There’s no way you’re going to get a factory AX chassis from AI or Mile High, the only way would be to get one secondhand like
@PBWalsh said. I’m not sure if anyone upgrading to my aftermarket chassis is de-bonding an AX...there may be a guy or two dumb enough to do it like I did haha. But then they will steal the AX buttstock, so you’ll end up paying a premium for the center section alone and then having to buy the $800 AX buttstock as well.
My advice would be to buy a demo AX now if you can swing it, or sell your AT to fund an AX. Or buy my aftermarket chassis haha. Sorry, I’m a terrible salesman.