Hi,
Here is a [http://www.partshere.com/hppartslist/hpparts.asp?part=B4L03A|link] to all the parts for your printer.
Scroll down to find:
'' '''Q5888-00002''' Glass Assembly - Scanner glass assembly'' - Glass plate on which the documents are placed to be scanned.
Here is a link to just one [https://www.impactcomputers.com/q5888-00002.html|supplier] of the part.
It is not a recommendation ot use them. It is shown to give an idea of the cost of the part. There are other suppliers that may suit you better. Just search online using the part number ''only'', to get results.
Here is a link to the ifixit [[Topic:HP Officejet 4630]] guides which may be of some help in replacing the scanner glass.
Hopefully this is of some help.