You are unlikely to find a PSU that will have PCIe power for more than 4 GPUs; and some flagships will only handle 3.
There are several cheats before you return cards (bear in mind the popularity means that you might wait weeks before you replaced them). Better to start with the ones you *can* run then change your approach because of a cable. You can get your fans sorted and tweak your miner in the meantime.
1. Use y-cables: PCI-e 8 to 2 by 6+2 and PCI-e 6 to 2 by 6 are available on eBay. There is no magic tying GPUs to PSU cables, as long as you are sensible in distributing the power and observe the PSU rail envelopes you should be fine.
2. Make up/rearrange your own cables. *Be aware* that there is no consistent modular PCIe power standard (ie Antec cables will fritz a Corsair and so on) Can be hairy - but you can pick PCIe power connectors apart using the two jewellers saws trick.
3. Use multiple PSUs.
Just to be different, I make up a set of bus-bars
Have you got 270 or 270x? These are pretty lightweight on power - I have several Gigabyte 270x which I have running at 450khash/s each - I liked the overspec cooling