hi henry,
I too have a 450D and I put a plastic screen protector on it like the one you are describing!! Go into any good camera shop and they will have them.. I got mine out of a black package (don't know the name).. they come in the 3inch size perfect for your use but I got the big ones as I also had a friend who wanted some!!
its been on since day one and is great.. keeps the screen pristine!!
josh
I just found this link to what you want I hope its ok to post on here
http://www.digitalcamerawarehouse.com.au/prod4188.htm