Can I guess you shoot 120 film?

Your only option is Portra 800, however, perhaps the new Portra 400 may be worth a stab.

I normally shoot 800 films at 640 and I'm currently experimenting to see if Portra 800 overexposed by 1/3 stop is better or worse than Portra 400 underexposed 1/3 stop. Perhaps that's something you could look at too.