patSS/00

iTrader: (6)

Are there any variable rate front springs (for fbody) that are non-lowering?

JD_AMG

There are currently no aftermarket springs for these cars that don't lower it more than the stock springs that I know of, front or rear. The closest will be something like a (SLP).75" drop or (hotchkiss)1" drop, while everything else will be more.
The question here is why would you want a variable rate spring? Are you assuming they will ride better, while handling better as well? Because they probably wont...
If you want ride quality stick with the stock springs and some good shocks, you would be amazed at how well they can ride and handle with proper shocks.

patSS/00

iTrader: (6)

Well there are variable rate rear stock height springs, in fact all the listings I see (like on rockauto) for rears are variable rate. The fronts are the opposite, no variable rates. As for ride quality, I'm doubtful that shocks alone will improve things on bumpy roads (but I'd be replacing shocks along with the springs).

JD_AMG

Yes those are factory reproductions, not aftermarket. Interesting that they only show the variable rate springs as many of these cars got the constant rate rear spring. Maybe they aren't variable rate but just labeled that way for some reason.
And you'd be dead wrong. Good shocks(not cheap autozone replacements) alone will make more of a difference than anything else suspension wise assuming everything is in proper working order, including the factory shocks. The factory decarbon shocks are the #1 weak link in the suspension when it comes to ride and handling, its how they are valved, so even brand new out of the box they are junk.
Your springs probably don't need to be replaced, as they don't wear very fast at all, unlike bushings or shocks. Generally when the springs are worn you will notice them sagging.
Either way if you are looking to improve ride quality just come out and ask rather than assuming you need to replace your springs, or need variable springs. What you probably need is good shocks, fresh rubber bushings, and decent tires on a wheel that isn't overly tall (at no higher than 30psi, you can play with the psi to get the ride you want).
Is better ride what you are looking for? What suspension mods if any, do you have now? What size wheels/tires and what brand tires?