Where is the source code of acos_nat.ko (a GPL'd kernel module used in RBR750)

Does anyone know where to find the source code for acos_nat.ko (distributed as part of the RBR750 firmware?)

This Linux kernel module contains a .modinfo section that lists its license as "GPL".  It also calls ip_route_output_flow which is marked EXPORT_SYMBOL_GPL in the Linux 4.4.60 kernel.

Therefore, it must be distributed under the GPL - but I haven't been able to locate it in the tarball available from the NG website. Does anyboy happen to have information where the source code of this kernel module is located?