That really looks like a standard denim shirt to me.
48 seconds of searching found this:
https://www.ebay.com/itm/284384587466?h ... Swhudg~WgGYou'll want two, because the pockets are rather unusual. Remember: a collar can be reduced in size, but not easily expanded. A lot of 80's dress shirts had narow collars like this, as the narrow tie was cool then (I had a few of both), so you can try searching vintage chambray vintage denim, vintage oxford, which all have a similar look- at least close enough. And watch the buttons- you want standard buttons (even if the wrong color), because many have snaps and you can't convert snaps to buttons, but changing to a closer match button is easy.
The skinny guy looks to be wearing a dress shirt, possibly a thinner oxford cloth.
https://www.ebay.com/itm/334242580804?_ ... %3A2563228Start digging!