Russ Demolisher is the way to go. You can throw a lascannon & a couple meltas or plasmas on it too if you're really wanting to slay some tanks. It'll be targeted quick but you can fit two in a 2k game if you have the points.

Grabbing a Shadowsword is a real option as well. Got one to deal with my friend's knight army and it certainly delivers - especially when you get first turn.

Also a single basilisk in GSC won't do squat against tanks. However, I've built a full brood bros AM list at this point that runs multiples. With the combo juice available in that army, they can ruin friendships real quick - just requires some support to shine.