So despite some small bubbling, this attempt was unsuccessful. In contrast to the thumbnail this is what my first attempt looked like - some small amount of flow but most of it was coming through a visible defect in the graphite. After that I started thinking a little more about the mechanical connection and ground a chamfer into the graphite to provide some dovetailing + two rings of grooves in the plenum which allowed for actual positive mechanical engagement of the graphite.
I ordered some cheap rectangular pieces of graphite through ebay, printed a plenum, and epoxied an NPT push connect fitting into the plenum, and that to the graphite (the actual first one was just a square plenum with no positive mechanical connection and urethane CA which at ~40 psi shot the graphite across the room. You can buy it new in small quantities but there are also plenty of cutoffs used by machine shops for cutting injection molding tools. There's an abundant supply of graphite available on the internet that's used for machining sinker EDM tools. One incredibly cool application is in Dan Gelbart's video on the single micron tolerance lathe he built out of granite parallels and air bearings. They're generally used in high precision applications (semiconductor fab, linear motion in CMMs, >60k rpm spindles).
If you're curious what air bearings are - they're an alternative to plain or rolling element bearings that use a fluid (air) interface to allow for frictionless constraint without part to part contact.
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