1. What is the retail price of a Gopan in Japan(yen)? Is it a fixed price?
Its about 30,000 yen online, or more retail.
2. Are there still Sanyo made Gopan being sold? Or only the Panasonic Gopan is sold now.
You can find old stock Sanyo machines, but I think they are now all panasonic branded.
3. Where can I buy a Gopan? Besides Hokkaido, I will have a 8-hr transit in Tokyo on my return flight.
Most electronics stores will carry them. Try the big bic camera in Sapporo.
4. Is there an option for international usage. My country uses 240V or would I need to use a step-down transformer for it.
You will need a step down transformer.