I looked into this some time ago... JJ array chips are a commercially available product... just send money. Apparently one of the bigger issues is making reliable contact to the chip that can survive thermal cycling. I doubt that they are any more demanding tolerance wise than other semiconductor devices. The problem with using high-temp superconductor JJ arrays is with the grain boundaries of the HTS material... but the Russians have made HTS JJ arrays and standards. At the time, there was a company that was very close to releasing a commercial liquid nitrogen cooled standard. I don't remember any of the companies that were involved with any of the arrays, standards.