1. Download the manual on
http://www.tamiya.com/english/rc/manuals.htm
2. Look up the part number - 13404036
3. Look on eBay and Google with the tag 'Tamiya 13404036' - on eBay make sure to include the description.
eBay has only a single hit, but Stella Models has one in stock currently.
Maybe I'm lucky with my timing, but are these parts really that difficult to find? If so, just contact Fibre Lyte, I'm sure if you help supply a sample component or a high-resolution scan with one or two basic measurements, they'll be able to list it on their website as a component they can manufacture on-order
And besides Stellamodels, the website
http://www.modellbau-seidel.de/ has loads of Tamiya parts that are hard to find elsewhere - I couldn't find a few 201XMW-specific parts, but they've had many 'standard' 201 parts in stock in the parts, so they may be able to help anyway when you'd contact them.