Yeah decent MK5s are getting scarce now, especially ones with all the desired factory options. So good luck with the hunting!
It seems the newer Golfs aren't as robust as people first thought, which is hardly surprising given the cost cutting and planned obsolescence culture we now live in, so stick to the MK5 if you can. However, VW's 10 year obligation for parts availability expired 8 years ago, so expect some things to be permanently on "back order", or just flat out obsoleted.