SQL Server 2008R2 - how to install replication components
You might get away with using the eval ISO.

Try download that, burn it to a disk (or mount it by other means) and see if it will cooperate. It'll certainly contain everything, assuming it is as happy to be used to update your licensed install as it is an eval one.

EDit: I've removed the link as it was incorrect. It looks from trying to search on their site that SQL 2008r2 eval isn't available direct from MS any more. You might be able to find it elsewhere though.