Recently I wanted to know the IP of our Chromecast device at work. It turned out to be easy; you can do it on the shell with avahi-browse since Chromecast responds to MDNS requests:
$ avahi-browse -vr _googlecast._tcp Server version: avahi 0.6.31; Host name: mogiedyne.local E Ifce Prot Name Type Domain + eth2 IPv4 Chromecast7400 _googlecast._tcp local = eth2 IPv4 Chromecast7400 _googlecast._tcp local hostname = [Chromecast7400.local] address = [192.168.178.18] port = [8009] txt = ["rs=Local content (Tab)" "bs=FA8FCA5D2078" "st=1" "ca=5" "fn=Chromecast7400" "ic=/setup/icon.png" "md=Chromecast" "ve=04" "id=d24c55f64e1afc0ff2dfae5dea0f47e2"] : Cache exhausted : All for now