You can find this at the SHQ Miniatures company in UK.

hey Brad

Wouldn't it be much easier to just create one yourself, in modelling clay or a piece of wood as a base, covered with a little plaster for texture?

It'll be a lot cheaper, you can make whatever type of bunker you want.
there's a lot of pictures and even schematic plans to be found online.
You can even paint them in just about every colour or camo scheme, as some were even painted as houses, with fake windows...

give it a try mate, you'll see the result will be much more rewarding than just buying one..

brgds
warvos