Peterbilt & Kenworth still make cabovers, but I don't know if you can actually buy a K100 or a 382 anymore. Most of the COEs offered by Kenworth & Peterbilt are medium duty and they use the DAF LF cab. Kenworth offers the K500 for severe service, and that uses the DAF XF105 cab.
The US Mfg's stopped building cabovers when the clean exhaust emissions were coming into effect. The Argosy was the last model cabover built, and you can't even get them anymore. There wasn't enough cabover sales volume to re-engineer and tool up to create the airflow space needed for the much hotter running emissions engines. When the length laws were deregulated in 1980, cabovers were no longer needed, cost more to build, and many freight companies were loosing drivers to fleets that ran conventionals.