Yep. That's one you have to make.
It's some kind of modified piece. The carriage bolts are too. Just standard ones, but ground down on one side.
I looked around a lot for one of those (I had one) and ended up using nylon washers from the hardware store.
But it would be easy to fabricate, especially if you have one for reference. It's just some tubing with a taper cut into it.
On mine, the bottom of it is also at an angle. But I think might have been a defect.