...
Is there any other place like 7822 in the galaxy, containing so many O-class stars?
Yes. There are a few O type clusters around but not many that densely populated.
One that stands out is the 2MASS J023xxxx cluster around
KM Cassiopeiae. It's a bit longer string of stars but it stands out in the sky from a few thousand light years away and has been mistaken for NGC 7822 more than once.
It's on the direct line between the bubble and the Heart and Soul nebulae.
There's a very large but diffuse collection of O types in the area of
Eeshorps EG-Y g541 containing a lot of black holes and neutron stars also. But because the cluster is spread out over a large area, it doesn't stand out in the skybox like 7822.
These other type O clusters I've found don't seem to have a lot of black hole companion stars the way NGC 7822 does.