Hey Ronin,
Sorry I've never used this site but since it's a copa classic version there are sites I have used that only sell legit Inter merchandise (since would include legit copa classic wear too):
On this site im afraid its only the captain version of the shirt that's available in short sleeve:
http://www.subsidesports.com/uk/lea...g-wear/copa-inter-milan-capitano-t-shirt.html
It does have the version of the jersey you want but it is long sleeve only (same for the away version):
Home -
http://www.subsidesports.com/uk/lei...rseys/1960-s-inter-milan-l-s-retro-shirt.html
Away -
http://www.subsidesports.com/uk/lea.../1960-s-inter-milan-away-l-s-retro-shirt.html
I can try and find other sites if these are not suitable. I will say that because the jersey you want is part of the Copa classics brand (and not an oficial Inter product if you will) I wouldn't think anyone would try to make a fake of it as they generally aren't that costly to buy anyway so that site might be fine and it's just that nobody here has used it yet to back it up is the only problem.
This site has the jersey you posted and can also verify its legitimacy:
Short sleeve version:
http://m.uksoccershop.com/p-14922/inter-1960s-short-sleeve-retro-shirt-100-cotton.html
Long sleeved version:
http://m.uksoccershop.com/p-14921/inter-1960s-long-sleeve-retro-shirt-100-cotton.html