Is there anything wrong with mixing different brand springs?
say for example whitelines in the rear and jumboz in the front?
I ask because whiteline only stock rear springs for my car, but no longer stock the front but they did offer dobinson(spelling) springs for the front. They said that they should work well together
a spring is a spring. if its the correct rate and instaled height (and of decent quality) then it shouldnt matter what the brand is. getting an off-the-shelf matching front/rear set should be too hard between brands me thinks.
Maybe you could keep the springs you've got and get a set custom wound to suit at the back by any spring manufacturer you like.
A standard linear MacPherson strut coil at any rate adn length you like shouldn't cost more than $200-$250.
Note: Many spring manufacturers (for my car anyway) wind quite modest off-the-shelf spring rates, even in 'sports' or 'low' configurations. These springs will work thus adequately with OEM dampers but not increase spring rate significantly.
For example, the only two linear rate coils I could find off-the-shelf for my TA22 were Dobinson (~90lb) and Lovells (~115/105lb) The car will go on the road with these Lovels coils and modest dampers as a baseline before further revisions are made. Ultimately I think I could approach spring rates of around 140+ for regular street use with weekend track use.