This site has many (but not all) of their kit instructions scanned. Some of them offer Japanes and English.
http://www.1999.co.jp/eng/
This site also has some instructions scanned also.
https://www.scalemates.com/
But you may just want to google the kit name instructions to see if they exist online if neither site has any luck for you.
F is for FIRE, That burns down the whole town!
U is for URANIUM... BOMBS!
N is for NO SURVIVORS...
- Plankton
LSM