New OE spec fork springs can be ordered from https://www.cmsnl.com/, eg. https://www.cmsnl.com/products/spring_5117117c00/ (not sure if this is the correct spring as there were multiple matching models for GSXR-750) Replacement usually requires some special tools, but can be done in approx 1 hour per shock. Or you can ask your local motorcycle shop for price for replacement. When replacing springs, it is adviced to replace the teflon coated guide-bushes, oil and dust seals and oils.