YOKIVE 25 Pcs Brass Ferrule Fittings, Compression Sleeves Ferrule Ring Assortment Kits, Great for Air Water Tubes (Brass Tone, 8mm Hole ID)

EDIT: Found something else that is similar as well, maybe this will work: https://www.mcmaster.com/product/92921A013 It doesnt seem they exist online, but there are tons of off the shelf things that are close enough to work with some modifications! Amazon has 8mm led holders, which will work with some epoxy or something to hold it in place. Here is a link to one of them, im sure you can find some in brass as well, though these are chrome. Additionally you could buy the 6mm LED holders and drill it out to 7mm if you have the tools to do so for a precise fit. Another route I could see possible is to use compression fittings for pipes. One way to do it would be to buy standard compression sleeves like these and then cut them in half to get a flared ring, and another way would be to buy fittings such as these and live with them being a little taller than the ones shown in the picture.