Brandon Carlo and Rob O'Gara are the two that are likely the closest. Both are big guys (Carlo is 6'5", and O'Gara is 6'4"). O'Gara is more polished as he is older and played 4 seasons at Yale. He's a rock back there, but likely grades out as 4-5 shutdown defenseman.
Carlo is a little more intriguing because he is much more athletic and has much better foot speed. He is younger and skinnier, but has a higher upside.
There is also Matt Greyzlyck, a BU grad, who is similar in style to Krug. He's looked bad in preseason, but was Team Captain at BU and has a lot of offensive talent. He is likely a longer term project as he needs more strength to develop as an NHL defenseman. Krug is much stronger than he is, which I think separates the two talents by a wider margin.
There are others, but those are the three big ones.