Line lock install help

[Ackattack]

I'm installing my brake system, including a line lock solenoid. My problem is the 1/4" brake line has a fitting on it that is 9/16-18 thread that is supposed to thread into the proportioning valve.

I'm wanting to install my line lock solenoid after the proportioning valve, so I need a 9/16-18 inverted flare female to 1/4" inverted flare (I think it's 7/16-? thread) adapter.... But I can't find this fitting anywhere.

The other option is to cut my brake line and install a more common size tube nut for a 1/4" brake line.....but my lines are stainless steel and I don't have a double flare tool that will do stainless steel.

Anyone know where to get an adapter like that or have another solution?