Caradco no longer supports the spring counter balances required for my double hung windows. They are a long spring that attaches to the window with a plastic slider. I am desperate and will consider any alternative.
Here’s a trick if you can find a place that sells this oddball type of hardware & you still have a working spring.
You hook each candidate spring to your original spring and pull slightly.
If each spring extends equally, the candidate may work.
But don’t pull the candidate beyond its elastic limit, where the spring metal is permanently deformed.
You might even hook together two candidate springs to extend their composite length.
You may have to make a metal substitute for your slider.