Shanks' dream is Kimbrel and David Bednar (Pittsburgh). I'm not sure either would cost a whole lot in terms of prospects -- especially if you took on most, if not all, of Kimbrel's contract. If you took on Kimbrel's contract, you'd need to either unload a bad contract here (and add a decent prospect to the pot) or try to get Will Smith traded. You cannot have two relievers make roughly 30 million on next year's payroll.
Given the fact that the entire pen needs a makeover - starting with designating roles for each guy and only using them in that role - I just don't see any of the big names since AA is still trying to nibble around the edges and doesn't seem convinced that this team is good enough to push anything other than marginal chips in.
Maybe there would be a chance he could get Yimi Garcia included in a Marte deal since Miami continues to be embarrassingly cheap, but Alex doesn't appear to have any interest in moving Waters or Pache.
Bednar, Ryan Tepera, Andrew Chafin, Mychal Givens types seem like the most we can expect, and I'm not sure simply taking pen management responsibilities away from Snitker wouldn't make the situation as much better as trading for one or two of those guys would.