Seems to me there are some questions to ask for each individual case.
Do you have air ride? It's unlikely there will be anything from the aftermarket. Integration would be very difficult and there could be liability issues if there are situations where the parts don't play nice together.
Do you have the magnetic shocks? Also unlikely the aftermarket will recommend using their systems. GM set up the system to work with their configuration. Any changes to "crutch" the ride height under load will not likely play nice with the programming the engineers set up for the shocks. You would effectively be changing the spring rates and perhaps ride height.
Do you have neither air nor Magneride? Even if the aftermarket doesn't list your vehicle as an application, in this case I'd say you should be able to sleuth your way to a solution since it's all mechanical. Moog and other spring companies have listings for their products that will tell you spring dimensions (diameter, height, spring rate, etc.). Look for something with your dimensions, but a slightly higher spring rate, or maybe a progressive rate spring. An alternative would be airbags that fit inside the springs. Racers use them all the time to add some spring rate to a specific corner of the vehicle when conditions call for it.
Hope you find something that works for you, assuming you just can't reduce the tongue weight a little bit.