I'm searching if there is some Maxscript function to get the plugins path, but i could not find anything.
If that helps, your function can be improved a bit, getting the Max version automatically:
getFileVersion(@"C:\ProgramData\Autodesk\ApplicationPlugins\ForestPackPro" + (maxversion())[8] as string + @"\Contents\plugins\" + (maxversion())[8] as string + @"\ForestPackPro.dlo")