Since I didn't want to chop / cut my stock needle spring, I found out that the springs you find in a Rear Sliding Damper & Brake Set for Tamiya Mini 4wd (15198) are a perfect fit.
Here they are shown compared to the original spring
When put together, it is two coils less than the original, one too many than I hoped for.
If you are familiar with these springs, the black one is the soft spring, the silver is the hard one.
Putting my airbrush back together, it wasn't as bad as I expected. I've put the tension setting to maximum. There is a significant reduction in trigger tension, and the best part is, it had a longer trigger pull compared to the original spring.
If the original spring gave you 1:1 feedback, this one is, I think, in the zone of 3:1 or 2:1.
Compression Ratio being:
Trigger pull : Needle retraction
Why the certain effect? The black spring has to compress first before it gives a good push to the silver one.
I'm still trying to find a sort of bushing to place in between the springs so I can match the original spring length.
Lessening the trigger tension can simply be achieved by adjusting accordingly.
Found a suitable bushing from an insulated wire connector. Fits perfectly!