Setup Phono on Mark Levinson No. 28

I brought Thorens MKII 318. I tried to setup with ML 23.5 and 28. Somehow the sound is very soft and not loud. I need help from audiophile guys.
I own a ML-28 and have an OC-9 cartridge from Audio Technica. The setup should be straightforward if you follow the instructions provided by Madrigal/Mark Levison. There are dip switches inside the chassis that allow you to alter the phono stage gain. Check out the .pdf owners manual on the website and it will provide complete instructions on how to change the gain for your specific cartridge.
I have a problem with my ML No.28. Is anyone knows where can I buy the knob of the tape selector? the second Q, where can I buy the phono stage for ML. no28.