I have not seen individual Sailor nibs for sale anywhere. They are different from Pelikan nib-feed units that are interchangable and widely available for individual purchase. The Pelikan is a single unit; that is, the nib and feed is built as a single unit that easily screws and unscrews from the section end of the barrel containing the piston filling system. The barrel and section in the Pelikan is a single unit.
I have a Sailor 1911 mid size clear demonstrator with the 14kt nib. The 1911 pen is also known as the Sailor Classic Profit Fountain Pen. It is available in a medium sized pen with a 14kt nib and a larger, fatter 1911 pen with a 21kt nib. It has a cartridge/converter filling system so the section unscrews from the barrel.
The medium size Sailor 1911's with 14kt nibs are quite similar in size and characteristics to the Saphoros. The larger 1911 Profit with 21kt gold nib also is basically equivalent to the Sailor Professional Gear except for design and appearance.
I did unscrew and disasemble the nib and feed from the section of the 1911 with a Fine 14kt nib for adjustment. Be aware that the nib and feed is not built as a unit. The nib separates from the feed after unscrewing from the section. As you reassemble and screw again the nib and feed back into the section you have to be very careful about the proper and correct alignment between the nib and feed. It can very easily misalign as you work it back into the section, so don't try it unless you feel able and do it assuming the risk of messing up the nib, the feed or both.
Sailor also has other exceptional nibs designed by nib Master Nobuyoshi Nagahara. I have a larger 1911 model fit with a 21kt Cross Concord Emperor Nib. This is truly a wonderful pen. Writing with it is a very enjoyable experience for me. The design of this nib is quite complex and different from the regular nibs. I won't mess with it and rather send it back to Japan or to a true expert if it ever needs fixing.
Enjoy your Sailor Saphoro. It is a very good pen.