Your probably going to have as tough a time finding CCM P-45s as you will P-38s if strictly talking retail off-the-shelf. Even pro stock is tricky, what's out there is limited and it goes pretty fast. Both curves are discontinued at the retail level. I guess there is the custom-order route, I've never been down that road so I can't speak to it.
They are similar but different. The P-38 is definitely larger, the lie I believe are different (5 lie for the P-38, 5.5 for the P-45 based on my own sticks). The P-45 is a smaller blade.
If your going to switch from the P-38, probably better off choosing a curve still made at retail, probably a P-88 would be the closest.