The UCSC build danRer10 should be at http://usegalaxy.org, but I don't see it right now. I will find out why and reply again.
I will also add the UCSC build danRer9 to be included for the next round of indexes (July time frame). Progress can be followed here for new additions: https://github.com/galaxyproject/galaxy/issues/1470
Meanwhile, either can be used as a custom reference genome. Instructions: https://wiki.galaxyproject.org/Support#Custom_reference_genome
Best, Jen, Galaxy team