I've a Andreani Cartridge Kit for front suspension - according to Andreani it should fit all 98-03 FZS 600 models. It's brand new, old stock, non original box. I have the fitting instructions on a PDF to email. It is not the current Andreani kit but is 'similar' to their model: 105/Y08. It has Andreani standard linear springs. if you need stronger springs then there are several suppliers/options for changing.
More details on n Ebay: https://www.ebay.co.uk/itm/143600637075
More details on n Ebay: https://www.ebay.co.uk/itm/143600637075