I did some additional measurements on my group.
The group can only accept a portafilter with a outer diameter of 71.8 mm and 80 mm on the ears.
I have been browsing portafilters untill they started dancing before my eyes, but failed to find anything suitable.
The Gaggia portafilters seem to fit, but the ears are (annoyingly) on the 14.00 and 19.00 position.
So to summarize, I need a p/f -straight ears- with the following dimensions:
A: max 80 mm
B: max 71.8 mm
C: max 62 mm
G: max 6.5 mm
H: max 29.5 mm