I put V2 and V1 up here, some people like one or the other, so you have the option. Check V2 here
https://www.prusaprinters.org/prints/882-prusa-i3-mk3-led-bar-holder-v2
Original from here: https://www.thingiverse.com/thing:2856776
Remixed for my light, mines more square (bought here, it's 15mm square) https://www.amazon.com/gp/product/B06Y3Y16R6/
Should slide in very snug, so be careful or use high infill (the gap portion can break)
I used PETG for mine (PLA should work but it might be brittle)
edit: So I realized the small little arms that push into the printer Z axis break easily. So, I created this little screw that should fit inside the hole. Put them here: https://i.imgur.com/OlGvlosr.jpg
The author hasn't provided the model origin yet.