Would an embedded switch module work in your application, rather than an ASIC?
Sixnet makes a 6 port managed switch on a small PCB that you can integrate into your system.
ET-5MS-OEM Industrial Ethernet Switch
(I know you're looking for a basic unmanaged solution - but perhaps the default or some other hard coded configuration will work for you and you wont need to worry about it).
EDIT: They make an 8 port gigabit version too now: ET-8MG-OEM Industrial Ethernet Switch.
I have gotten some of Broadcomm's data sheets before. Technically I was working as an OEM but my yields were low - 10-20PCBs (custom contract design work). I had to sign an NDA and we had to blow some smoke about working for a fortune 500 company etc to get them to cooperate though. Is this for any commercial application, or hobby work? Perhaps you can get an application engineer to help you out if you pitch what you're trying to do to them.
EDIT: If you end up going the route of adding a UC, you could use several WIZNET chips (e.g. W5500) in MACRAW mode.
Your MCU would need to poll each of the devices, maintain a list of the MAC address associated with the device at each port, and direct the data accordingly.
Or perhaps put a cluster of these guys (W7100A) on the same bus.