You have a router with a modified firmware by your ISP. I bought mine and it had the original firmware. Last time, I contacted broadcom to release the source code and they gave me a negative response. Maybe you can try to contact broadcom again.
I tried with many of vendors and couple of ISP to release the source code or at least the SDK and toolchain. However; they simply do not care or not responding.
I think the open source and software community should do something about this, but I see less interest to take actions against GNU Licenses violators.