eBay
Please ask for further specification if this is crucial to you, I'm happy to look it up, but I'm not an expert on Apple products so I've just copied this from the "About this mac" part of the computer. The computer works brilliantly but all my other devices are non-Apple so I'm selling it to replace it with one of those - at 44 I'm too old and crotchety to run 2 different systems. 
Macbook Pro Retina 15 inch Mid 2015
Processor : 2.2 ghz Intel Core i7 (not sure what 'generation' it is, you'll probably know this better than me, it's a Mid 2015)
Memory : 16GB 1600 Mhz DDR3
Graphics : Intel Iris Pro 1536MB
The cover is marked slightly as I put it in my briefcase to take home from time to time, but it's not heavily marked or chipped or dented. I don't have the box it came in, I do have the original Apple charger cable. Everything works 100% and the sound is brilliant.
If you have any questions call me on 07904 413684 during office hours as I have no mobile reception at home.