bla bla bla, somebody do all my research for my half baked project for me, while I ignore all alternate suggestions and reason itself, bla bla bla.
You even got a scuba suggestion, takes 10 seconds to google:
Compressors | ShoeBox Compressor << ShoeBox Compressors - The World's Smallest & Lightest 4500 PSI Compressor
I don't know about compressing flammable fluids, you might have to do your own experimenting in an outbuilding, and buy term life. You pays your money, you takes your chances. ~$2000 including a fibre tank.
googling for "shoebox cng" returns what you already know:
bla bla bla, google already.