Is there a MAC based wallet available for PWR?
Not at this time. NIST5 coins contain very very old code base with a super outdated QT PRO build routine. 
Our dev team spent an enormous amount of time to correct that and we did produce a cross-platform build routine for the code base and to my knowledge no other NIST5 dev team has ever pulled that off.
With all that being said the labor required to do this for MAC is huge and I am not saying it will never happen but I can say don't expect it right away. In the meantime please consider using a VM with the linux wallets.. other users have used this approach and so far it is working for them.