It could be possible that your looking for a XP-G3 660nm dominate photo red that doesn’t exist. I dont see it listed in the datasheet.
They list the XP-G3 as 645 typical dominate, which if you look at their spectral graph which includes 660nm but it is just not the peak produced by the led.
I used one here in a modded Thrunite Ti3. ~~ENDED~~ [US Only] Free Thrunite Ti3 v2 on Thrunite.com (with $5.95 shipping fee) - #112 by moderator007
They can be found loose at Digkey, link is in that post.