CNG is available in Islamabad at the following, There maybe others, so please let me know, so that i can add them on list.
UPDATED LIST : 24 May 2019
Blue Area PSO
F-7 Shell (They sell CNG slightly cheaper, so there are small queues sometimes)
G-10 Shell and G-10 Lillah CNG
G-11 PSO
H-8 Total
I-9 PSO
Expressway - PSO, Koral CNG, Kaleem CNG
Expressway - Near Khanna Bridge, AR, Faiz, Attock and Shan.
Faizabad bus stop
if u drive from stop towards stadium chawk, 1 more on the left
at stadium chawk another 1 on the left
another 1 on same road 1-2 kms ahead
No gas load sheddings, no waiting queues.