I have an interior sidewall groove that needs to be rounded -- it's like a thread, but cut with a scoop instead of a vee shape. Luckily, it's in 6061 aluminum, so not very hard to cut.

The lollipop cutters I can find all look like the left of this picture, but I need something that looks like the right. Ideally, 1/4" diameter, where "diameter" is the diameter of the round part, so the total width is more like 1/2" or whatever adding the center shaft will make it.

Attachment 423116

Where can I find a cutter like this?

(The closest I've found is McMaster: https://www.mcmaster.com/2820a74 -- but ... 6 flutes? Not for aluminum, surely? Also, 3/4" shank is hard to get into the TTS holders I have, which top out at ER20 and 1/2" Weldon.)