I am working on a project using springs. What is the maximum load per deflection of springs available in market?
There is no sensible answer to this. Springs are designed to have a relatively high deflection relative to their to ultimate strength. Once you want very stiff springs you can just use solid bars of steel.
The trick with spring design is to end up with a product which has a specific set of properties and it is possible to make arbitrarily stiff or light springs. What may be more difficult is combining a desired stiffness and capacity with a particular set of dimensions and lifetime.
Equally any answer may also depend on what you define as the difference between a spring and a structure as all solid materials are essentially springs for a given load range.