You can use plot configuration manager "PlotConfigManager" to get all the plotter devices available for AutoCAD. “PlotConfigManager” has a property called “Devices”, which provides the access to all the devices. Below code shows the procedure.
[CommandMethod("ListPlotDevices")]
static public void ListPlotDevices()
{
Document doc = Application.DocumentManager.MdiActiveDocument;
Editor ed = doc.Editor;
PlotConfigInfoCollection devices = PlotConfigManager.Devices;
foreach(PlotConfigInfo info in devices)
{
ed.WriteMessage(info.DeviceName + "\n");
}
}