You can also look into switching materials, since different metals and alloys have different elasticity characteristics. https://www.engineeringtoolbox.com/y...lus-d_773.html
The spring manufacturers definitely offer a lot of their designs in numerous options. In terms of the massive spring companies, the people reselling them for trem springs don't ever specify really. There's not an actual factory that just does "Guitar Trem Springs" though, half the components in trem design aren't actually specialized shit. The saddles and stuff sure. But a lot of the bolts and springs and shit like that they just order from other massive companies. So if you go directly to the people the guitar companies are buying their springs from you will see more options than looking at guitar parts sites.