However, ensure that the Kollsman is not a periscopic because it sure ain't easy to hand hold and then there's the power supply!?
Ideally, a WWII Mk.IX would suit, but heaven knows where you'd get one. Most are in museums or collections.
There are marine sextants which have a bubble attachment and a google search would bring one up. Just remember that aviation sextants usually have a two minute averager [I think the Mk IX had a 1/2 minute option switch] to counter aircraft movement. I haven't heard of recent marine sextant use in the air.
G'day
