Bridging Firewall

Does anyone know of a firewall that can reasonably protect things in a bridging environment?

I'm faced with a situation where I am forced to deal with a (vertical market) system that requires Layer 2 adjacency (no way to route across a router), and simultaneously am required to put a firewall in place so that only authorized traffic can cross between the two portions of the network. Also, there's a strong desire for the equipment to be suitable for an industrial (IEC-60495 type) environment.

Bandwidth requirements aren't that high (100mbps total throughput) and the system is isolated from the internet. Also, something that's COTS is strongly preferred, otherwise I'd just whip up something with linux and ebtables.

I've looked at the Checkpoint 1200R, but it doesn't seem to have the ability to filter between the bridge ports. I haven't tried to lab up the rugged Cisco ASA, but from the documentation I'm not convinced either.

TL;DR: I'm in need of a firewall that can work between two bridged ports. I don't think they exist.