Im not talking high detail custom. I thinking a "we need a shoulder holster right now" custom. The stunt mans rig looks pretty cheap so I wonder if they just sewed some leather and elastic together. I honestly have not seen a holster close to the Skyfall one.
I definitely think it is a great possibility. I too have been thinking that it very well be custom made by themselves too. Exactly how you stated, "we need a shoulder holster right now" kind of thing... However, I still think that the holster in the photoshoot picture is a galco. My conclusion would be if you want one that looks like the one in the photoshoot picture, get the galco executive. If you want one like the stuntman has.. visit your local crafts store and make it yourself. This is all a big headmash though.
For one I think they are custom made because the one worn by the stuntman and the one worn by craig in that "360ish" picture looks like crap to be honest. It looks like a cheap POS, I've tried to bite my tongue on it because it could turn out to be the opposite but thats what it looks like to me from the pictures. :lol It looks exactly like something you would throw together with some cordura, buckles and sewing a piece of leather together to fit a ppk. It looks terrible.. The other possibility is that they just bought a cheap airsoft holster.
I know I've seen that style of shoulder holster worn by the stuntman before with the strap going behind the back but it was years ago and I can't remember what it was and I cant seem to find one online either. It might have been a blackhawk serpa that I saw years ago.. but the problem with that is it uses kydex type hard case holsters not leather. So that can't be it.. Unless somebody bought a holster that didn't fit the ppk, and they just removed the holster and threw on a piece of leather to fit it.
Now if that's not confusing enough, if you look at the picture that was posted on here from the book, you will clearly see that there is no gun in that holster. And that holster looks like a small well made one.. You once again see the nice looking front leather strap that was seen in the photoshoot picture and matches the Galco. But yet another problem.. Not only can you see that there is no gun in the holster but you can see through the holster.. and it is a significantly large hole at the end. The holster worn by the stuntman looks like it was sewn all the way through with no hole on the barrel end.. there isn't not a very good shot of it but that's what it looks like to me.. and if there was one it certainly doesnt look like the tip would have a hole large enough to match the size of the hole in the one in the picture of him jumping down on the train (the one posted from the book). Now the Galco executive ppk on the other hand does have a hole on the end.. and it certainly matches the one from the picture of the book, in addition to the photoshoot one.
I haven't really read up on the modifications they did to the PPk for the movie, but if they messed with the grips or beaver tail significantly this could certainly cause the gun to not fit in a ppk fitted holster.. which could lead to holster problems and the need to custom make or retrofit one. So it could be a, "uh, our gun doesnt fit the holster kind of thing". But if they custom made one to fit it.. why would they not put in the holster?
Yet another possibility could be that they love to have Daniel Craig in extremely fitted suits. This does not go well with shoulder holsters in reality. It causes an inevitable bulge.. so this could explain why the holster is rarely ever seen.. perhaps because there was none.
In conclusion, with the limited evidence we have, I'm gonna call it and say it was a Galco Executive that was the primary holster, used in the photoshoot and in the train scene, and it is the one that was meant to be seen. Some other crap was custom made or retrofitted for the stunt scenes. Hopefully some more pictures or info will come later on to confirm this, or discover the real holsters.