Mine was done literally two days ago, by my normal servicing dealer. Likewise it was done as part of a regular (35K) service. When I called in for the appt, I identified it on my list of to do's alongside the normal service. They confirmed they had one remaining part set on hand at that time. The service advisor did want me to come in promptly, which seemed to reflect the availability point.

So, did you identify the work ahead of time with them and did anyone check on the part set? Or, did you really just assume and then head in? While there may indeed be a local supply issue, it seems to me the issue likely starts with your local dealer and the appt. set up. That should be addressed w/ them.

Maybe you want to call the 800 Audi number and get to the A8 concerierge type? Maybe another dealer has the parts like mine did, and they can be transferred?

I would be disappointed too.
The issue with the fuel rails the dealers should of had the parts due to the recall Audi sent out to the customers.

Fuel pressure damper recall done last August on my A8L 4.0.
Ever since, the fuel gauge shows less than a full tank (3/4 full) that corrects itself over a week or so. The miles to empty range indicated is
correspondingly inaccurate and also corrects over a few days.
I've been waiting for it to self cure. But no luck so far.

Just me, or am I missing something? A dealer tweak?

The recall didn't apply to my '17 MY - but I did have the same fuel misreading issue and it turned out to be faulty sensor that needed replacing. There is also a TSB associated with it.