Just start with contacting industrial supply houses that make hydraulic hoses. You may have to talk to a few of them to finally find the right one but these hoses are nothing more than a gas hose with the correct fitting swedged into the end of them.

I usually just contact a farm supply house that makes hydraulic hoses for tractors and if they can't make them they can usually direct you to someone who can.

Just take in your old hoses and ask if they can make them.