Buchanan Radiator, 252-1273.
It's a small shop but he does good work, tell him Tyrel Manley told ya to try there. He may be able to get it done for ya if he doesn't have a bunch of work right now. I don't know how common the core is but if a place there has it in stock maybe see about getting it and having him do the work.
He delivers mail daily and this is a side job for him, so he does it lots of nights and weekends.