Hi,    The catalog refresh to be the latest, therefore the firmware will not be listed on older version. You may need to download the firmware from our support site and import it from DRM. 
I'm having an issue updating iDRAC firmware on M640's in OMEnterprise from 3.2x or below to 4.0. The resolution I've found is to update the iDRAC to 3.3x first, and then update to 4.0 through OME, which works. Question is - how can I create a repository in Dell Repository Manager with iDRAC version 3.34.34.34???
Create Repo with specific firmware version(s)