General Steel Castings Corp (GSC) began manufacturing the Commonwealth 8' wheelbase, 4-wheel, swing-motion express truck in the late 1920's. It was assembled from a one-piece cast-steel frame with integral pedestals, drop equalizers, and 33” rolled-steel wheels. Single inboard-mounted brake shoes acted against each wheel. Applied to numerous types of head-end cars and to virtually all General American Refrigerator Express wood-sheathed 50' express reefers built in the late 20's and early 30's, the trucks remained in high-speed service until as late as the mid-1960's.
Athearn makes the only GSC Commonwealth Express truck in N scale (specifically designed for their Pfaudler milk cars). For whatever reason, Athearn simply lists these as "N Scale Trucks" (catalog #90639) -
Fine N Scale and CS Models both make generic diecast express trucks that are at least somewhat "Commonwealth-esque" -
Athearn - wheelbase 12.62mm, frame width 16.05mm, wheel size 33", axle length 13.7mm