Pretty much any turbine will work. Being air (low temp, non corrosive/reactive) opens up a lot of options.
A
https://www.amazon.com/dp/B0002YVBK2/?tag=pfamazon01-20 converts compressed air into shaft power, that could be coupled with a very small generator.
For a bit more power there are larger options, some I've read about in small
ORC systems:
http://waset.org/publications/6420/efficiency-of-compact-organic-rankine-cycle-system-with-rotary-vane-type-expander-for-low-temperature-waste-heat-recovery (An engineering student at MIT adapted a used car aircon pump, can't find the paper right now).
https://en.wikipedia.org/wiki/Rotary_vane_pump
Tesla turbine
https://en.wikipedia.org/wiki/Tesla_turbine
Screw compressor
https://en.wikipedia.org/wiki/Rotary-screw_compressor
Scroll compressor
https://en.wikipedia.org/wiki/Scroll_compressor
http://organicrankine.com/?page=orc_automobile
Even a supercharger (lobe pump):
https://en.wikipedia.org/wiki/Roots-type_supercharger
Nearly all pump & compressor types can generate shaft power when operated in 'reverse' (ie a fluid is forced through them).
There are plenty of manufacturers around but you'll need to know your working pressures, flow rates etc first. Or you could just scavenge some compressors from a junk yard and wing it.
The real question is why?
How is it that you have compressed air but need electricity?
You are much better off, in terms of cost and power generated, to generate electricity from whatever source created the compressed air in the first place, eg if your air compressor is deisel, then buy a diesel generator, you'll get maybe ten times as much electrical power per litre of diesel burnt, much cheaper in the long term, and probably cheaper capital cost too.