You can dupe them yourself with a fairly minimal setup. It will be an initial investment, but if you will be doing it a lot it might be worth it.

Another option is scanning the chome and then re exposing a new one from the file using a film recorder. This also lets you do any necessary spotting, contrast tweaks, and/or color correction in the computer. The one I am used to using (Polaroid) has backs for 35mm, medium format, and 4x5.

DR5 offers the film recorder service. I am not sure if they can do 100% analog copies. I'd give them a call.

I know that nothing interesting or extremely useful like this can be done at the big lab in L.A., A and I. They are a decent lab and I am glad they are there, but they only offer very run-of-the-mill services. If I could easily get analog transparency dupes made, I would shoot chromes almost entirely for color.