If you really want, you can use the data in r134aPropertyTables.mat to calculate the cp for both the liquid and the vapor phases, using the definition of Cp = dh/dT, where h=u+p*v, and p,u,v,T are all available in the table. You may find more information on the data structure of this .mat here: https://www.mathworks.com/help/simscape/ref/twophasefluidproperties2p.html
However, the Cp calculated this way may not be what you need on the two-phase fluid side if phase change happens inside the heat exchanger (which I suspect does happen). The latent heat part, instead of the Cp*dT part, is usually the majority part of the total capacity. So the Cmin=Cp*flow equation you mentioned is valid only for the TL side, or the 2P side if no phase change occurs.
