3Racing do a spring set that comes in a box with pairs of springs part number SAK-49 Damper Spring set. These are designed for the Sakura Zero which uses the shorter shock.
Another option is the new Ride mini springs which are to be relaesed soon or another alternate is to purchase the SpecR spring sets which come as Hard, medium and Soft. These are short springs like the Tamiya offerings. The SpecR items have four pairs of springs per rating. For soft has T6.25, T6.5, T6.75 and T7 at 1.4. PNo for Soft set is SPR022-MS.
I am using these springs on the rear of my Sakura FF car. This has the short shocks also. I still using the 3racing shocks but have considered fitting the M chassis length TRF shocks.
You can also purchase different shock shafts for the shocks.
Another option would be to use standard size springs with 1mm down spring retainers.
Hope that helps.
Calvin.