I've been doing a little more digging. the SK-7100 is available all over the web. I've found it available from $79 down to $34.
$34 in Beige but check with them. maybe they have it in black by now.
Now here's the good news. A UK site says that the SK-7100 is is Twirp compatible. http://www.twirp.com/index.htm
So it's got a published spec and protocol. the dongle at Twirp looks the same as the SK-7100. and there are spec validation tools that show the packets, scan codes, etc. Unfortunately the validation tools are $400 but maybe we can borrow a copy from someone until we find out what's going on in the gateway kbd.