Stanley Hardware
From Wayne's Dusty Box of Words
Cap Iron screw: 5/16-18 BSW Frog screws: #12-20 Tote & Knob bolts: #12-20 Tote Toe screw: #12-20 Frog Adjusting Plate screw: #12-24 Frog Adjusting screw: 1/4-24 American/Unified; Brass Adjusting nut: 9/32-24 American/Unified (left-hand thread); Lever Cap screw: 9/32-24 American/Unified. Much of the rest on planes is also #12-20
If you do a lot of restoration, it's probably worth your while to track down a tap & die in that size. It's pretty rare, but you do come across them occasionally.
