Seems as if the Platinum batteries are out of stock everywhere!  

Have a shoot coming up in Haiti and need to get my hands on some.  Any insider info on future stock dates.

Also, I assume the Regular pro batteries are identical other than color... is this assumption true?  

Yes you can use the MP battery on the MPP. If you've got this shoot, then p/u some of those.

https://www.dji.com/mavic-pro-platinum/info#faq

Try some droneshops , they might have bought mpp batteries in bulk. Here in the netherlands some webshop shops still have them in stock.

If you're really stuck, Apple sell them as well.

Yep - the original Mavic batteries work with the MPP (the internals of each battery are identical in fact). Plenty of those around but they obviously don't match the MPP new colour. There are very few places that have the MPP battery now - stocks are obviously low after the Christmas sales.