You can't...
ISO-Media catalogs really don't work. This has been an issue since 1.0 of vCloud (VMware is very aware, just does not seem to be correcting it, I assume not to many customers are complaining about it)
Media (ISO ect) need to be copied into the VDC that they will be used from. So if you have lots of providers (different clusters) - you need to get this copied to all of them... (Even if the disk storing is something like NFS that all the hosts can use without issue).
Please point this out to your VMware rep /and/or support; we have been begging to have this fixed for two years now.