You might want to talk to Adam from
Inkmed. He got me four generic encoder strips for use on our Mimaki printers, and they were
cheap.
They come as straight bands, so you have to put in the mounting holes yourself, but trust me, it's worth it for the price you pay. Not sure if the JF series uses a similar encoder strip, but that would be my first stop.
Edit:
Sorry to the domestic suppliers I use! You know who you are, and you're absolutely the best. There's really no contest here though. The bad guy in all this isn't the Chinese manufacturer, it's Mimaki, for robbing us blind over a piece of plastic with lines on it.