The only way to do it tax and duty free would be to go to Akihabara yourself, buy the goodies in person (paying sales tax), and get a receipt. Then submit the receipt to the relevant tax authority to get your sales tax reimbursed (there are companies that will help you with this for a fee). Then you take the goodies back with you in checked baggage and hope you’re under the personal limit for importing goods, otherwise they’ll hit you with the import duty anyway.