Bring a checked suitcase or buy one in Japan.

Hello!

Going to Japan next month, we are taking a small bag and carry on bag each as we don't want to carry a checked bag around for the whole trip and it costs around £60 each way to check a suitcase. I am however considering to buy some Japanese knives whilst in Tokyo along with clothes / souvenirs we are thinking we might need the extra suitcase. Is there anywhere in Tokyo/Osaka that you can buy a half decent suitcase that's either a carry on size or bigger for around 5k Yen?

Any advice appreciated – also if anyone has knife store recommendations that would be great, my budget is 20-30k per knife.