Finding a supplier for this product is proving to be very difficult. I understand that your best source would be a Japanese company but from the research that I carried out, it seemed like Japanese manufacturers of Kotatsu are not online-based.
I have found a retailer of Kotatsus and other Japanese products that you might want to check out. Here is the link to their website: Link hidden: Login to view. They use authentic Japanese materials for their products. You may contact them and enquire if you can get quantity discounts. Other products that they have (like Japanese Tea) can be purchased wholesale or in bulk quantities.
You might also want to check out this Malaysian furniture manufacturer: Link hidden: Login to view I have found online that they do manufacture Kotatsus as well although it is not in their e-catalog. You may contact them and enquire about this. You could also enquire what payment methods they accept. Please only pay through safe methods like credit cards and PayPal.
I have also found a dealer of Japanese products in Australia. Although they are retail store, they offer a best price guarantee. The website is Link hidden: Login to view They guarantee authenticity of products and they accept international orders and credit card payments.
Note that these suppliers are not in our directory so we cannot make any guarantee but we have checked that they are established companies.
Hope that helps!
All the best,