These cars came out some time in the 90s and were originally sold by MDC/Roundhouse. Circa 2005, Athearn acquired all the old MDC/Roundhouse cars and re-issued these in Athearn packaging. Roundhouse sold them individually and in packs of 12. Athearn sells them individually and in 5-packs.
These cars come in three different flavors - flat end, peaked/round end and peaked/angular end.
I'm not sure what specific prototype these models are based on, but generally speaking, 40' hoppers like these were first introduced in the 1950s and saw service on many different roads through the 1990s.