japanese bathtubs (also called ofuro) are supplied without equipment or machines of any sort

To be honest, building a tub is more similar to naval carpentry than a normal plumber job. We do not supply any machine or pump equipment of any sort.
I recommend to find locally a pump and cartridge filter. If you replace the water every 3 days or so, you might skip the filter. About the disinfection: do not use chlorine.
Ozone seems to be popular, personally I would recommend a salt chlorinator. Please ask a pool equipment dealer near you. I had a client who used 'Aquapure' in a small pool and was very satisfied. It is a product available in the US. See: http://www.jandy.com/html/products/chlorinegenerators/aquapure_faqs.php