Have a look at the KW-V30BT. It indeed does play FLAC files.
It shows up on the jvc.co.uk detail site. One of only 4 head units that does play FLAC files. The others are KW-V50BT, and the other 2 single DIN units (KD-X310BT and KD-X210)
Hope this helps. I'm also in the market for a FLAC deck, and I'm planning to make a move on the KW-V30BT.