How to put Exhaust Hose for Air Conditioning Unit Through Window?

[thewinelake]

We want to install some portable aircon units in the office.
They have 150mm flexible ducting for the exhaust.
We have single glazed windows where we can make a hole to let the air out.
However, there doesn't seem to be a simple plastic moulding that either:
a) Is a simple grommet to line a hole with and we'd pop the ducting through.
b) Is a proper louvred vent that has some kind of sandwiching mechanism and a spigot for attaching duct.

Must be? Surely!