I need some of this part but I’m struggling to find any sets they came in:
BrickLink calls it Technic, Pin Connector Toggle Joint Smooth Double with Axle and Pin Holes.
It comes in a number of sets listed here.
Here is some detail of the sets containing the part listed in order of year released (newest first). The green highlighted sets are currently still available on Lego Shop.com (US) at the time of this answer:
Since most sets didn't/don't come with very many of this piece, you're best bet is probably sourcing them from Bricklink or somewhere similar. They're about .20 cents (USD) or less on Bricklink.
They are also available for purchase individually at Lego Shop.com for .42 cents (USD):