Based on the two references that I checked, it's 6. Staffel.
According to Steenbeck's "Die Spur des Löwen":
- I./KG 26 was based in Norway for the entire period from Jan 1941 to Nov 1942.
- II./KG 26 was based at Eleusis and Iraklion (aka Heraklion) from May to Nov 1941, with 6./KG 26 being relocated to Zilistea at the end of Aug 1941. (FYI, Zilistea is now known as Zilisteanca, and it's approx. 8 miles NE of Buzau.)
I also checked Larry deZeng's excellent "Luftwaffe Airfields 1935-1945" compilation at
http://www.ww2.dk/lwairfields.html, which states that 6./KG 26 was actually based at Buzau airfield in late 1941, not Zilistea.
(Although Zilistea was one of the largest and busiest German airfields in Romania, I would tend to go with Larry's research, based on the comprehensive operational unit lists that he provides for each airfield.)
Hope that helps,
Leon Venter