Go to a dive shop or divers website. I believe Bauer are good manufacturers. if in a shop ask about them, they do mobile compressors but they arent cheap. You want one for diving as these will have filters to stop crap getting in your tank. trouble is that a compressor that can max out at 4500 is going to be straining like a bast*rd to give that out, so life expetancy will be reduced. It will also take a while.
I think they are around £3000.
Hope this helps.
Gaz