The most difficult things to customise are the Tsuka (Handle) the Habaki (collar) and the Saya (scabbard).
These are tailor made to fit each individual sword and are NOT interchangeable.
Changing a Tsuba is EASY...
Most Tsuba are interchangeable.
If the hole is too small, then you carefully use a file...SLOWLY and file it bigger where it needs to be.
If too big, then you use a punch and distort the edges of the tsuba.
Lot's of nice Tsuba out there...
Come over and try:(these are readily available to order)
A Hanwei - Summer Plum Tsuba
A hanwei - Winter bamboo