A flat acron is one which has an angular defecit of zero. All flat acrons yield acrohedra (if coplanar faces are permitted) simply by attaching two such acrons with a ring of squares.
Trihedral flat acrons
6-6-6
8-8-4
10-5-5
12-6-4
12-12-3
15-10-3
18-9-3
20-5-4
24-8-3
42-7-3
Tetrahedral flat acrons
4-4-4-4
6-3-6-3
6-3-4-3
6-4-3-3
6-6-3-3
12-3-4-3
12-4-3-3
Pentahedral flat acrons
4-3-4-3-3
4-4-3-3-3
6-3-3-3-3
Hexahedral flat acrons
3-3-3-3-3-3