I order out instead of trying to do it here, but my old knowledge says to always start with RGB, which has more colors than CMYK, and let the printer software do it's thing. Of course, if it's already CMYK, changing back to RGB won't bring back the colors that were dropped when converted to CMYK. There are probably some profiles you could create for it, but how tedious that may be I do not know, but I suspect it's quite a task. Maybe some of your vendors could help with that. Here, we just take whatever we have, and send it to our favorite vendor, and they come back looking just about exactly as we send them in. I may have had maybe only 2 jobs in the last 2 years where that was necessary.
Steve