In the output, the estimates of these contrasts appear at the part of "Model Results" which is before "Standardized Model Results". So, I am wondering the estimates for these contrasts in the output is standardized or unstandardized? Is it possible to get standardized estimates for these contrasts?
First you have to decide if you want contrasts based on standardized coefficients or if you want a standardized contrast (divided by its SD). Let's assume the former (the latter is automatically obtained as the z score in Model Constraint). You are showing formulas with a*b which implies that you want to standardize a*b wrt the SDs of X and Y in the X->M->Y chain. So you need to be able to express the variance of Y from your model parameters. You do this by labeling parameters in the Model command, and then use those labels to computed the Y variance in Model Constraint. The X variance is obtained simply by the Model command labeling: