I would go to the car buildersweb sites for what they are offering try Evans, Thrall, johnstown, Greenbriar and maybe somebody else can post some others.
Neither Evans nor Thrall have not been around for a while. The four current manufacturers of boxcars are Gunderson (Greenbrier), Trinity Rail Group, Freight Car America (formerly Johnstown America), and National Steel Car. American Railcar Inc builds cars, but not boxcars.
Its seems like the most common boxcar type manufactured in the last couple of years is the 60’ inside length, excess height, exterior post boxcars. The most common door arrangement for these seems to be double 8’ plug doors, although there are also single plug door, single sliding door, and double sliding door.
I forgot about Gunderson’s subsidiary Gunderson Concarril. I went to Greenbrier’s web site to make sure I was not forgetting about anything else and found Gunderson GIMSA and that Trenton Works appears to be a sister company of Gunderson.