Replasment for Mullard Long Plates?

There are still a few NOS 12AX7s available. If I were you I would pursue a search. I saw some Sylvanias as a group of 5 NOS NIB for a fair price. There are still Mullards but like you said striaght labeled newish looking ones are almost non existant. I use 5751s for most 12AX7 duties but these too are scarce and not always the best tube for your application. These Noval double triodes do seem to last a long long time, it may be justifiable to invest in a good pair.

Wolf -do yourself a favor and check out Audio Asylum Tube Asylum and do a search for the Gold Lion (Russian/re-issue/current production0 12AX7. Or you can just call Jim McShane who sells a lot of the GL tubes about them. He is a very striaght shooter. He has a website as well that you can do an internet search for. My understanding is that the GL 12AX7 is somewhat warm, sounds very good, is well made, and on the expensive side. That last sentence was 22 words is that enough?

Wolf
The AA threads can be displayed in two formats. I prefer the one they call Classical. You will get many more specific answers regarding the Russian GL. Make sure to you look in the "Tube Asylum". It isn't all that painful honest.
The old Philips tubes from Holland are essentially European Amperex 12AX7s. They have a devoted fan base and are desirable if in good condition. I don't have any Philips Holland, so I can't comment specifically on their sonics sorry.
I see your curiosity has been piqued regarding Old Stock, roll with it. Sorry again about the pun.

I thought the only real old stock 7025s are RCAs, but I am not sure. Both me and another tube rolling friend have tried the 7025, and weren't impressed with the results. Therefore Wolf, if the 7025 is definitely your tube of choice I think you should go with something new. That said, my experience with old tubes has been a lot like Mike's. Remarkably the worst tube experience I had was with a KT-90 new production of course. It blew and took out a socket, resistor and then burned some section of the wiring.
New production 12AX7s are really quite good and it is really not necessary to buy old stock to get good sonics. I think as little as 5 years ago that wasn't the case. BTW I have only discussed tubes with people interested in the matter. I don't have a sign or T shirt advertizing what I have in my collection.