How do I identify and replace unusual screws?

I’ve got a desk held together by these really strange screws below. The tapped end goes into one end of a joint, the plastic piece goes into the other end of the joint, and then the head of the screw goes into the plastic piece, with an additional screw (shown in bottom picture) to hold it in place. The pen is for scale, with the screw about 1.5 inches / 4 cm in length.

While I’m not optimistic that someone here would recognize these two pieces, is there a general process for identifying parts like this? I’d 3D print a copy of the plastic piece if I had some way of reproducing all the grooves inside it and getting a matching screw, but I have no idea if these types of pieces are standardized, and if so what they’re called and where I’d look.

Thanks in advance for any help here, you guys are awesome!

Edit:
It’s not IKEA. I brought it to them and they said they’d never seen the parts before.