Mate I live in japan, and to be honest, I order most stuff from the uk, with legal restrictions on knives, and the general style of glamping above camping means the equipment out here is very expensive and lightweight. The pricing means that it is cheaper for me to order and ship from the uk than to buy locally.
Kitchen knives and scissors are all mainly mass produced stuff now. The hand foraged stuff is very very hard to find and will make you cry when you see the price. There is no bartering out here, and certainly not with foreigners. Xenophobia is rampant out her especially in seki were most of the metal work is done. Most people will flat out refuse to deal with foreigners. Second hand markets are unheard of.
You may not believe me, but I have been here over two years now. My Co worker has been here for nearly 30. He works at a rubbish tip twice a week to get his hands on old japanese kitchen knives. But you cannot buy from a tip. They will not sell. He worked his way in over a few years. Good luck enjoy your trip.
If you are worried about laws, don't. It's pretty much the same as the uk. If it's in a bag, wrapped up you'll be fine. Traditional swords are 100% illegal/impossible to buy unless you have an art dealers license.
Any questions. Feel few to pm me.