You will need to Open a ticket with the account in which u want to request the CDMA SIM.
As far as having 2 SIMS, one CDMA and one GSM, I do not believe that is possible for the same line, as the CDMA SIM works very differently. It is tied to the exact phone and has to be registered with R.W. network in a different, more exclusive way than GSM. Also, I do not think you can have 2 active SIMs for one line, or at least I have never seen any wireless provider be able to do this.
May be possible to keep the “other” SIM active as a different line, and swap it in when needed, but then u have to pay for that separate line, and deal with keeping a tiny SIM floating around, that is easy to lose.