They do claim it doesn't exist. It's not an argument they emphasize in their public messaging, presumably because it's such obvious nonsense, but it's one of their core arguments in their lawsuit challenging all California handgun restrictions (https://storage.courtlistener.com/recap/gov.uscourts.cacd.85...). "Microstamping technology does not actually exist in any commercially available application on a handgun" (p. 11), and therefore it's the California law requiring it rather than manufacturers refusing to implement it that's depriving California consumers of access to modern handguns.

That's not a lawsuit by a gun manufacturer, those are regular private citizens and the "California Rifle and Pistol Association". So far as I can tell, that's not an industry lobby group, it's a private interest group although I'm sure the manufacturers like them.

That changes the above quote. It's not a gun manufacturer claiming they can't find anyone to microstamp their guns (though not dispositive of the same), it's a citizen saying that commercially no one sells microstamped guns.

If you expand out your quote, it neatly explains what I would wager is the reason why no one sells microstamped guns:

"AB 2847 also imposes an additional amendment to the UHA: for every semiautomatic handgun that satisfies the new one location microstamping requirement (in addition to havingCLI and MDM) and is therefore added to the Roster, the State must remove three (3) grandfathered semiautomatic handguns from the Roster, in reverse order of addition. However, this has not yet occurred because microstamping technology does not actually exist in any commercially available application on a handgun."

In other words, if a manufacturer decides to make a new microstamped model then 3 models that are likely still in production will become illegal. It's a losing proposition for the manufacturers. There's no money to be made by creating a new production line to build microstamped pistols if it's going to shut down an existing line; it's a bunch of money to re-tool factories to sell to the same people the shut down line was already selling to.

Without getting too into the weeds of politics, it's exacerbated by it being California. Whether you agree or disagree with the goals of the policies, they do change the requirements for guns very frequently relative to other places. I can understand manufacturers being reticent to set up new production lines to comply with policies that will probably change again in the next 5 or 10 years.

My reading of the lawsuit is that they think this was the intended end state of the bill. Require new guns to implement a feature, ensure that implementing that feature will generate financial losses, and now no new guns get made but you can point at gun manufacturers and say you didn't ban them the manufacturers just won't comply. I'm not totally sold on that, but it is a remarkably poorly written bill when the incentives the bill sets up run exactly counter to the intended goals.