It may be easier if you could identify what it is you consider vintage. To me vintage is a bit lower in contrast and shows more grain than more modern films. It also has a bit lower response to red so that reds come out a bit darker. Of course that is my perspective and may not be your own. You should also remember that to some degree that vintage look is also the result of the format used for many old photographs. Large format sheet film is well known for a much larger tonal response than is possible with 35mm.
It sounds like the look of Efke 25 in your Leica Standard is what you are looking for the closest I have come at this point is by exposing Ilford Pan F 50 at EI25 and developing it in a low contrast developer. I have been having decent results with D-23 (which I mix myself) which produces a lower contrast negative if I use it at 1:3. Believe it or not, if I hold off for a week or so in developing Pan F 50 I get and even softer look, but I haven't been able to get consistent results yet so I wouldn't recommend it. Reducing the amount of agitation will also lower contrast to some extent. There are a lot of tricks you can try but it does take some fooling around with your options.
Unfortunately I haven't yet found a real good replacement for Efke film, I am really going to miss it when I run out of my stockpile. One thing you may want to try is an orthochromatic film like Rollei Ortho 25. That really is a more vintage style of film and you may like the looks you get with it.
Like Ian mentioned, I think you can probably get the type of look you want with about any film if you do some experimenting with developers, times and agitation. I am currently playing with Arista EDU Ultra 400 (Fomapan 400) exposed at EI200 and developed with Beutler 1:1:8 with some interesting results. Fomapan 400 will naturally exhibit a bit more grain than Ilford Pan F does and EI200 works quite well with the available shutter speeds in the older Leica cameras.
I also notice (or at least I think I do) that my uncoated Elmar 50/3.5 seems to have some influence on the results. The pic below was exposed in my Leica III with a 1935 uncoated Elmar 50 on AEU 400 at EI200, then developed for 12 minutes in Beutler 1:1:8. I like the print quite a bit but the scan may not do it justice. The other problem is that there is a bit more cloud detail in the sky than I would expect from the vintage look.