Hmmmm, I think it's going to depend a lot on the agency and their needs.
If you're relocating to a different state & lab and want to go into Firearms exclusively, you're only going to be eligible for the entry level positions (i.e. positions that require no firearms examiner experience). You would be competing with the college grads, but at least you have lab experience and hopefully some courtroom testimony by now, so I'd like to think you'd have a bit of an edge.
The other possibilty would be to find an opening in a lab that would do cross-training, as Richard mentioned -- perhaps a small lab that could use both a DNA analyst and a firearms examiner trainee -- if you're still willing to devote a significant portion of your work hours to DNA for the foreseeable future. As labs become larger and more specialized, a position like this will probably be increasingly hard to come by, but there still may be something out there... somewhere....
If anything opens up like that at my little lab, I'll let you know!