Dowel bracket fixture
I'm not sure if this exists or not.

Probably not.
However, you have an X Y Problem

I'm trying to build a piece of furniture that I can take apart quickly/easily and set up again in another apartment.

Commonly used solutions include
Furniture bolts

Mitre bolts

Knock-down fittings
AKA furniture blocks

Cam lock bolts

Woodworking Joints
See https://woodworking.stackexchange.com/questions/3305/creating-a-speaker-stand-using-only-joins/3306#3306