Can you set up mirroring for sql server reporting services?
Mirroring is for individual database.  For reporting services, you can user web server farms (AKA scale out deployment).  It will allow multiple servers in a cluster.  You will need SQL Server Enterprise Edition for this feature, though, as well as a load balancer (Windows has this or NW hardware like BigIP, etc.).  See here for more info:

http://msdn.microsoft.com/en-us/library/ms156453.aspx