Hi Slivver,
yes, the 1942 proof was carried out with Nitro powder. Consequently, it was safe then (!). If it is still safe to shoot, that is another question. I’d contact a gunsmith for checking the gun.
BTW: the 1942 repair proof wasn’t the only one. Marking crown/R indicates, that a reproof or repair was done sometimes in the Imperial times.
So, your main interest are European pocket pistol, huh? Nice, because I also do collect mainly European pocket, i. e. pistols made by J. P. Sauer until 1945.
A nice forum specialized in these European pockets is the forum of Jan C. Still:
http://luger.gunboards.com/
Check it out, I guess, you’ll like it.
Regarding the swivels: well, of course I am not able to tell you a source in the US, but swivels of Sauers are nothing special. Every standard (German) swivel will fit.
Regards
Martin