As far as I know it's no longer possible. Either from Media Encoder or Premiere Pro. The only way to export IMX is via an .mxf wrapper.
Running an older Mac OS (Sierra in my case) on my own work machines it is still possible to export/convert IMX30 into a .mov wrapper via Final Cut Pro 7 or via QuickTime Player 7 (Pro) - both of which will not work on latest MacOS.
I work in a Network TV environment where we used to deliver all SD content using the IMX codec using .mov from FCP7. Now that we've mostly moved to PC and Premiere Pro we still deliver any SD material in IMX but now using the .mxf wrapper.
It might be that your client *can* accept IMX in .mxf. Worth checking.
If not you'll need to track down an older Mac with the FCP7 or QT 7 Pro installed.