- Yes. OWC has an option: http://eshop.macsales.com/shop/ssd/owc/macbook-pro-retina-display/2013-2014-2015
There is the OWC Aura. It is still pricey and has a lot of shortcomings.
OWC make some they are more expensive than upgrading apples drives at point of purchase are only half as fast for sequential read/write and they don't support trim, so not a good bet. You can get them pulled from other machines on eBay but again you are better off just buying the 512gb rMBP in the first place.
- Only if they are original Apple ones and listed as such.
Good luck, just make sure you are looking at 4 Lane PCIE drives or you'll be taking a performance hit as that is what the 2015 models shipped with. Late 2013 and 2014 were 2 lane for the 512GB SSD.
Like Samuelsan2001 said, it needs be a drive specifically made for the rMBP because of the proprietary connector. More likely than not it's going to be a system pull but there are drives from time to time sellers claim are brand new.Probably not, unless they say for Apple they won't fit the proprietary connector or the space available for them in a MacBook Pro.