DIY solution available. I suggest to read entire post from beginning.
That Pegasus J2i Cage - Internal HDD Mounting
Alright, well, the 4xSSD cage and 2x3.5" are done. The STL files are here https://www.thingiverse.com/thing:4067905 From a printing service like MakeXYZ.com, The SSD cage is $85.90 to print and ship. Not bad when competing against $400. I haven't printed the 3.5" cage so do so at your own...forums.macrumors.com
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2019 Mac Pro Drive Cage by bwinter88
This is an alternative drive cage to the Promise Pegasus J2i accessory meant to be mounted in the 2019 Mac Pro. There are two cage designs; one to hold 2 spinners, and one to hold 4 SSDs (in the event you have a PCI card to connect additional drives)The power connector for internal drives in the...www.thingiverse.com
And for anyone looking to print that, just make sure you use PETG or ABS for it. PLA isn’t going to handle the exhaust from the CPU heat sink all that well.