I agree, very difficult to find, though they are equally rare during 1915, - each maker so far has the same number of reports. Roughly 9 each, though CGH has 10.
I could never find a VCS (any year) for sale that was in good condition. CGH seemed difficult too, though CGH are the most numerous of the three makers (I just had a hard time finding one in nice condition). Mark Wieringa once wrote that he found JPS the most difficult (nice), though was the easiest for me. I have had half a dozen JPS over the years, a couple of them pretty nice examples.
All the SUhl makers can be tough to find nice, Simson and the Consortium, even the sterngewehrs Dresden assembled can be tough in nice grades... a combination of low numbers and their comparative extensive use probably account for this. Saxony must have had to use their rifles longer, or perhaps they had the same grievance Bavarian's had with the Prussians, - I have read that at the end of the war the Bavarian's felt they carried a disproportional burden of the fighting (probably because they were more reliable at the end... it is also said in British summaries that some of the best (disciplined) troops they witnessed returning to Germany in 1918 were from Württemberg).