If you have a loose ball cup and cone BB you will not find replacement axles, so Annually, every spring is a Good Idea,

you will have to replace it with a cartridge BB if the spindle gets or has Pits in it,
spare axles have been discontinued a long time ago .

NB you can improve sealing by stacking O rings on the axle to press against the outside of the Cups , before you
put the arms back on, how many depends on axle length between the 2.