But sadly not these anymore.
From ;
https://en.wikipedia.org/wiki/Shin_Meiwa_US-1A"The US-1A was retired on December 13, 2017 when the last example in JMSDF service made its final flight."
"The aircraft has been replaced by the ShinMaywa US-2."
And from :
https://en.wikipedia.org/wiki/ShinMaywa_US-2 "It can be used as fire fighter taking 15 tonnes of water."
Now there is a Whiff - an Australian based US-2 or if Hasegawa doesn't brink out a Kit of this or you don't want to modernise this Kit then there is always this lead in :
"In 1976, one PS-1 was experimentally modified for aerial firefighting, with an internal capacity of 7,350 litres (1,940 US gal) of water."