Hardware store. The one closest to the engine is supposed to be a stud, not a bolt. It's also one size larger than the two outboard bolts. The two outboard bolts are 5/16 and the stud is 3/8.
this doesn’t say what thread , someone said above 5/16 18 thread at at least 3” long . My measurement they need to be at least 4” long . What thread is the 3/8 ?