Where can I get a part for a discontinued amp?


I own YAMAHA DSP A1 and I really love it. However, I lost the two knobs for input selector and volume control. Where can I get this? I don't even know their "official(?)" part names/numbers.
kyleestl
If it is available at all, a given part may be available here;

https://www.yamaha24x7.com/YamahaOMS/BasePages/Login.aspx?ReturnUrl=%2fyamahaoms%2fdefault.aspx