Lets do a simple math with what we know.
Foxconn daily production of iPhone 6+ : 140,000
25 days of production for launch day
140,000 x 25 = 3,500,000 total production x 0.96 for DOA = 3,360,000
3,360,000 split between 18 countries.
For the hopeful, say apple holds back 70% stock for the US market = 2,352,000 million
2,352,000 / 4 major carriers = 588,000 per carrier
588,000 x 0.5 half preordered = 294,000 total for first day sales
294,000 / 257 total apple stores = 1,144 total phones at an apple store available
1,144 x 70% held for retail stores = 343 per apple store / 4 carriers = 86 phones per carrier
Now if apple only saved 50% for the US market, number shrinks.... Make your choice when thinking this is like the iPhone 5s release in availability.