Funny you should mention the M³, I've got 3 of them in the works. Two in single-ended config (L/R/G), and one in full balanced (dual mono L/R, no ground). The single ended units are finished, tested, and awaiting final chassis modifications. Even having used unmatched JFET and MOSFET, they are a very sweet sweet sound when loaded with OPA604 @ 24-32vdc. Scope out nicely on my trashy Rigol too. I've spent more on the bloody chassis for the amps than I have on the parts. Custom panels are freaking expensive, and international shipping sucks.
Ti at AMB does sell the matched sets for the stuff that requires it if you don't want to do the matching yourself, and he ships stupid quickly. Same day in most cases. But if IIRC, the JFETs don't need Idss matching, they just need to be within a specific range. You're pretty safe just buying the parts from Mouser (Digikey/RS/whatever), with the expectation that the JFET and MOSFET are from the same batches, and will have generally the same characteristics.
I've got eight of the α24 in the works for a DIYINHK ES9016 8 channel DAC. Also something needing a chassis. One of the MD types would be freaking awesome for it.