I looked quite a bit but didn't find any delta effector mounts that I liked for an auto bed levelling sensor. The few I found were either too long, or didn't fit the thickness of my aluminum effector plate. I decided to try to learn Fusion 360 and make my own, and here is the result of my first F360 project.
I'm using the aluminum "End Effector for Kossel" from Robotdigg. It's the one they show with the square cutouts between the arm mounting points (which is where this thing slips in to).
The original version has a 3mm thick mounting plate to hold the sensor up. I have added a v2 version which bumps that to 5mm thick, which should be a bit stiffer.
The Fusion file is included, in case anyone needs to make changes.
I printed this in PLA at 0.2mm with a 15% hexagonal infill. It's only holding up a 18mm capacitive sensor so it shouldn't need much.