If you are a capable person, an auto engine can be converted to compress air.
125psi works out to be 8.3:1 compression ratio... most auto engines are 7:1 - 9:1 for petrol and 13:1 for diesel.

I've seen on UK tv a 2 cylinder motorbike engine used as an air compressor running off hydro... if i find any info, i'll add it on.

Do you have an idea of the amount of air you want at 125 psi?

The biggest hurdle I can forsee is the size of the blades to provide the quantity of air you require, as you'd need quite high torque to get the compressor going.

Also, compressing air is expensive in terms of energy used to compress air, and there is alot of energy wasted as heat from the compressor... an oportunity for co-generation?