Welcome.
Looking for the correct magazine is kind of like expecting to win the lottery.
Not only do you need the correct number, but also correct type/style magazine with correct acceptance markings. Then add trying to match the condition and it is nearly impossible.
It has been done, but only by pure luck and lots of it. JMHO.
The German army used lugers from all years in the second world war, your 1918 is as likely to be a bring back from the the second war as the first, again JMHO.