Please keep in mind that if you are purchasing parts in Tokyo, Japan, you will need to pay taxes on the products, and that you will not be able to ship by frieght. ONLY AIR MAIL is the way to go. For the Mugen SS sport suspension, expect around $300USD for airmail.
If your dad going to Tokyo, I would say that going to SUPER AUTOBACS in Tokyo Bay Shinonme. It is one of the easier places to find in Tokyo, but you better damn well know the subway lines or you will get lost. Dont try to take a cab from lets say Shinjuku/Shibuya to the SUPER AUTOBACS in tokyo bay. Taxi fares have insane pricing, so if you do take a cab, be expected around $900 USD from the downtown core (Shinjuku) to the SUPER AUTOBACS. For the train, it will take roughly 50mins, and change 2 subway lines. the cost for train will be around $20 USD.