There will be plenty of intact pressure vessels all around the plane that can be used to store steam (engine oil tanks, potable and waste water tanks even made of fiberglas, and last but not least fire fighting tanks with a squib still under pressure).
The problem is the boiler itself not blowing up. I would use a hydaulic piston as the boiler enclosure.
Course there are also all kinds of stuff in the shipping containers in the hold including tyres under pressure which could power the many micro-turbines like engine starter motors etc.
I bet if you managed to buy a scrapped B777 (Asiana) you could ship it to an island and populate it with volunteers to sort these questions out pretty damn quick.