Is there a database where I might list the phenotype of a certain rat knockout and/or search for other similar phenotypes?
There is a International Mouse Phenotyping Consortium, which has the goal of characterizing the phenotypical changes of homozygous knockouts for each of the 20,000 genes in the isogenic mouse line C57BL/6. The International Knockout Mouse Consortium is responsible for creating the knockouts and the two consortiums work together closely.
There is also a Knockout Rat Consortium, but I haven't found a Phenotype Change database for rats.