Even if your cousin finds the place, ordering can be a pain in the neck because they dun understand a word of English. Sometimes they need days to order stock, so your cousin need to be there long enough to go back to the shop to collect.
Most parts shop are out of the city, hence not very accessible via subway.
I do not know of any TRD
shop within Tokyo, can try Super Autobacs at Tokyo Bay will be worth trying: http://www.sa-tokyobay.com
Again, it's a little inaccessible, take train to Tatsumi station (http://www.japan.co.jp/~pbw/tokyosub.htm) (yellow line, south), then it's about 5 blocks distance by foot. Tokyo city map will be useful.
Within Tokyo, TRD
parts are normally available (or via order) from Toyota stockist. I find that the best way to locate the nearest stockist (with langauge problem) is:
1. Go to Amlux (Ikebukuro Station, red line north)
2. Approach the pretty looking Receptionists, yes they speak English.
3. Ask them for contact of a nearby stockist (and a date if possible)
4. If you can charm them, you can even get them to make the parts enquiry
5. Overcome langauge barrier and stock availability at the stockisthttp://www.amlux.jp/amlux.shtml
Important: get the parts no., model ready, manufacturer model no. ready. The stockist may end up refusing to order/sell parts if they know that your manufacturer no. is meant for export. Silly you may think, but they insist on upholding their service and responsibility in ensuring that they sell the right parts for local fitting. So either pop up the bonnet in Amlux showroom to get the local manufacture no., and tell the stockist "you stay in Tokyo".