NWSL once offered 45" square counterweight HOn3 driver sets, and they may occasionally turn up. Wiseman has offered the SSL kit (advertised but never sold under their name) for the NPC cab forward 4-4-0, which apparently used the NWSL drivers, also a chassis kit that included two pair of drivers. I do not know if either is still available.
Alan Gibson Models, in England, produces a wide range of OO scale drivers, and some of the smallest ones are suitable for HOn3. The current catalogue is available at
. Diameters are given in OO(4mm scale) feet and inches, or alternately in millimeters, so some conversion is needed: divide the metric diameter by 3.5 and multiply by 12 for HO inches. These drivers have 1/8" steel axles, engineering resin (delren?) centers and steel tires. Tires are available for OO finescale/EM and S4 "gauges", all 4mm scale but which differ in British modeling practice. OO/EM tires are roughly the RP25 code 88 profile normally used in HOn3, the wheels supplied with two axles. S4 are exact OO scale British SG. Wheel centers are a push fit on axles, so fairly easy to regauge and quarter. Crank pin holes are pre-molded, and crank pins use a steel screw from the back, with a sleeve bearing retained by a nut. Due to the very wide variety of counterweights used on British prototypes, these are omitted, so the user can provide an appropriate style.
The smallest drivers offered are 11mm, 10-spoke, scaling 37.7" in HO. Plain wheels down to 10.5mm = 36", on 2mm axles, suitable for outside frame engines, are also available.
Are there any suppliers of HOn3 drivers? I know Precision Scale has unmachined ones. I would rather not invest in a lathe and milling machine at this point.