You're talking about the part replaced in this LCD lens guide, right?
[guide|5042]
If you hit the "Read More" button in the introduction, the author listed two places to buy it.
He says:
"I found two retailers,
1. USCAMERA in the states, who were most helpful but i couldn't get there website to accept payment via credit card, they have an ebay store http://myworld.ebay.co.uk/uscamera/
2. Lehman in the UK. http://www.hlehmann.co.uk/ Again most helpful, they answered my many emails chasing the order, i was desperate to get my 5d back. I would stress that they are incredibly busy at the moment. If you want to communicate with them i suggest email through their website 'contact us' and ask for a call back. Very nice people to talk to."