Precision 3930 Caddy?

So, it's been a long time since I've bought a server, but I have literally never bought a computer or chassis that I couldn't install my own drives in.  But I recently snagged the new Precision 3930 to be the brain of a live music show.  I got it with an nvme boot drive and two empty 3.5 bays because I already have drives.  So I ordered it with blanks - in hindsight, I get that blanks aren't caddies (even though literally every chassis I have ever purchased had caddies filling up all the "blank" spaces).  So I jump on Dell.com to buy caddies....and I can't.  Support says they aren't available. 

I figure I can just grab some caddies from a different model...but I take a closer look at the "blanks," and they don't look like they have the same mechanism and spacing as hot-swap bays I've used before (yes, I know technically the 3930 has "cold swap" bays - they're similar sized caddies).  

I feel like I have to be missing something, because Dell releasing a product that you have no means of installing drives after the fact seems....odd.  Like...why even let me choose what size the blanks are if I can't buy caddies?  Is there another caddy that should fit into this chassis? 

(yes, they advertise the Precision 3930 as a workstation, and I have a consumer chip in it, but I still figure the Server forum would know more about bays like this)