Goya champroo is a dish from the southern island Okinawa. Champroo means mixed things in the island’s dialect.
About 20 years ago, goya (bitter melons) weren’t available in the main island of Japan. Only Okinawan weather was suitable to grow the vegetable. But I see them at many places in Japan now.
According to wiki, there are several varieties of bitter melons. The one I bought and used for the cooking was Chinese variety. The Indian variety is actually much closer to Okinawan variety. You can buy whichever available near your area.
I think you can find tofu easily at your neighborhood, and I am sure you can find a can of Spam, too.