Hi nathaphong33,
Welcome to the Apple Support Communities and thanks for posting about your issue here! We'd be glad to see if we can help point you in the right direction. We see that you had purchased a Logitech 4K Pro Magnetic Webcam from Apple previously. Now it seems that you're looking to purchase spare parts or a brand new one as it has started to give you issues.
For this, we'd recommend reaching out to Logitech which manufactures this product for further assistance. In addition, if this product is currently sold out from your local Apple Stores, you may be able to purchased it directly from Logitech instead. You may be able to reach their specialists from Logitech Support.
Take care.