I found two Jet gasstations listed for Leipzig:
Jet Tankstelle Dieskaustr 111, 04249 Leipzig
Jet Tankstelle Sommerfelder Str 58, 04299 Leipzig
Notice that the retailer search lists only 6 results per page, you need to click "weiter" below for further results.
But there are also
Jet gasstations closer to the border in Bautzen:
Jet Tankstelle Stieberstrasse 49, 02625 Bautzen