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Kenneth
You asked about spares for Hughes MkIX bubble sextants.
There’s no spares market for individual parts for MkIXs.  However, whole sextants still come up on eBay regularly. Unfortunately, there’re fewer good ones than there were 20 years ago. You just have to keep buying them until you find a good one.  Avoid the memorabilia merchants, especially ones claiming it to have been used in a Lancaster.  Such people have an inflated idea of value.  Look at the photos very, very carefully.  You’ll soon learn to spot the dents, scratches, pitting and fungi.  Then just keep putting in eSnipes and bidding low.  Eventually, a Bank Holiday, or the third to come up in a row, you’ll get one at a sensible price. 

I do know a man who has cleaned more MkIXs than most.  He’s probably reading this right now.  If you follow this link https://www.ebay.co.uk/itm/165394351300?hash=item26824584c4:g:Ql4AAOSwvb9g03di  and use the ‘contact seller’ function,  You might get a favourable reply.

One word of advice on any ex WW2 bubble sextant.  Unless your prepared to pay a lot of money to have one professionally rebuilt with every part perfect and live in an area of almost zero light pollution, don’t expect to see more than the brightest stars and planets at night.  Venus, Jupiter, Sirius, and Capella are about the limit with my MkIXs.  Incidentally, you don’t need the averaging mechanism on solid ground; it’s only there to average out acceleration errors.  It’s not quite the same sort of averaging as swinging onto a body afresh for each observation with a marine sextant.  
It’s also possible to convert broken 3V Hughes filament to led bulbs, but I’ve never needed to try it.  Always check the cotton wool inside the tiny pill box inside a MKIX case.  There’s often a freshly laid batch of 3V bulbs hidden inside. DaveP