I've dealt with this exact situation before, I guess I was blocking it out because it's SO annoying. Some folks would put this information in <dc:contributor>, and in fact several of my OAI sets do just this in their DC records. I suppose that might be OK, but the DC Contributor definition is "An entity responsible for making contributions to the content of the resource" and I don't know if I'm so comfortable calling "paying somebody to digitize this stuff and then asking another department to 'put it up on the Web'" "making contributions to the content of the resource." Some folks would put this information in <dc:publisher>, but again I'm skeptical. "An entity responsible for making the resource available" (DC Publisher definition) does apply to the digital resource. However, we're dealing with published materials here whose publisher for the print item can be an important access point. And we don't (nor does pretty much anybody) have a sophisticated mechanism in place for making good 1:1 principle records and linking them all together in a way that allows users to search on things meaningful to them and get meaningful results back. Putting our holding institution in Publisher in this environment would not serve our users' needs.
I started out using a hack I'd used before: put the holding info at the beginning of a <dc:source> field and add to the end the local call number so it fits the Source definition. But then I got annoyed at using what I consider a hack. So I started digging around. The Western States Dublin Core Metadata Best Practices made up their own element (currently called "Contributing Institution") and don't map it to DC. This is one of the very few elements they go completely out of DC for. The DC Libraries Working Group made a proposal in 2002 for a new DC element called holdingLocation, but by the time this proposal was reviewed by the Usage Board, MODS had gotten off the ground, so, the UB decision said to use the MODS <location> element instead.
So the DC solution to this problem is to use an Application Profile that borrows an element from another schema. But once you start doing this, the draw of DC (simplicity!) is lost. I'm probably just going to use MODS instead. Sigh.