Yikes. AndyMark does have some other solenoids not on their FRC page, but there isn't enough information to tell if they are rules complaint.
This one for instance:
http://www.andymark.com/product-p/am-2304.htm
That would work, but it isn't clear if it would be compliant. The page gives a different set of specifications from Festo's datasheet for that same valve. AndyMark's page shows a flow rate of 220 L/min with a Cv of 0.22. If that same ratio applies, the flow rate listed on the Festo data sheet for that same valve of 1380 L/min would be a Cv of 1.38 which wouldn't.
I'm also not clear about what NPT means. The rules state that 1/8" is the largest permitted, but that would seem strange given that the KOP includes 1/4" parts.