Hello, welcome to the forum.
It is unlikely that you will be able to source a crystal from the manufacturer, so your best bet is to purchase a generic crystal.
You will need a crystal press to fit the new crystal.
The old crystal will need to be pressed out (without breaking it as you need to measure it to purchase the replacement).
You will need a means to measure the crystal accurately, thickness and diameter. A vernier gauge is ideal. Sizes typically go in 1/10th a of millimetre for the diameter. It is quite easy to get it wrong even with experience, I usually buy the two nearest sizes measured, to make sure I have the best fit.
Good luck!