I just pulled the two bolts that I purchased from Premier 2 years ago.
Correct, they are not shoulder bolts. It has been two years

The shoulder bolts are elsewhere in the wing.
I paid $70 each, so the price has not changed too much in 2 years.
These bolts are made to a Cessna drawing (thus very low volume).
The gage length and thread length appear to be tightly controlled.
This is to ensure that the shank of the bolt rests on both brackets with the thread run very close to the bracket.
The thread length is short to control the length between the strut bracket and the wing frame.
A quick check of my supply of AN bolts could not find an equivalent bolt. The threads would be resting in the bracket, or the length was too long.
One of the big problems with AN bolts is that the gage length is not controlled, the length is.
Boeing designed their bolts opposite, we control the gage length because that is what you need to determine and then added threads on beyond that.