I do not know about AMOS, but we use this website to calculate Cohen's d. You should be able to fill in the missing data using AMOS and let the website do the rest.
you are mixing two different things: Cohen's d is a measure of the effect size / group difference in the sample (like a B or correlation coefficient), whereas p-values give information about the state of affairs in the population (refer mostly to the question "is there an effect at all?).
If you have a binary independent variable in SEM, then the path coefficient implies the mean difference between 0 and 1 in Y (the dependent variable). If you standardize Y, the coefficient becomes Cohen's d.