According to Tasha's Cauldron:

"This item replaces a lost limb: a hand, an arm, a foot, a leg, or a similar body part. While the prosthetic is attached, it functions identically to the part it replaces. You can detach or reattach it as an action, and it can't be removed against your will. It detaches if you die."

According to Xanathar's Guide:

"This artificial eye replaces a real one that was lost or removed. While the ersatz eye is embedded in your eye socket, it can't be removed by anyone other than you, and you can see through the tiny orb as though it were a normal eye."

In and around the Crowded Sea:

• There's a 25% chance that ordinary gear merchants will have one for sale for 150 dinars.
• Additionally, magic item sellers can have them for sale using my secret "shopping for items" rules. Expect to spend several days of searching, including paying money, and the price, if you do find one, is 500 dinars.

(They also show up on random treasure tables.)

This means that there are two ways: one cheap and easy (but only works like 25% of the time), and one slow, expensive, and risky (but works around half the time), and you can try both.