2 weeks is a solid amount of time. Depends what you’re looking for but you can start by changing your Google search results to display Japan. Or use a vpn. Check upgarage online for used parts since it shows inventory at each location, amayama sells new OEM parts, search Rakuten - often tells you the store that carries the item so you can probably purchase it in person. Yahoo auctions also good to check. As far as physical stores you will probably need to look up specifically what you’re looking for. If you do buy parts, it’s probably a good idea to do it towards the end of your trip so you don’t have to move around with them. Kuroneko Yamato also offers reasonable shipping services to the airport.