I'm gonna agree with Rubrick on this one.

As faldage noted, you get a lot of hits if you google "go by": but as ASp notes, many of them are verb usages; e.g. "I will go by the store today." However, even a search for "+a go-by", to limit the hits to noun usage, still gets 2350 hits, many of which seem to "fit" the usage we're discussing. For example:

http://grouper.ieee.org/groups/1159/2/minport.html: "T. Use linguistics’ or some other pattern recognition as a go by for developing standard" (appears to be from fall of 2000)

Edit: Earliest usages appear to be mostly from Britain or India, but often the meaning appears to be somewhat different: sometime "a test", and sometime "a dead letter". E.g, from August 3, 1998: "by then, the Indo-Sri Lanka agreement had been a go-by". From December 1996: Coverage of social areas is also given a go-by because news managers believe that readers are more interested in "hard" news than in 'soft' news.
http://makeashorterlink.com/?D2755286
http://makeashorterlink.com/?Z3C52486 (near end)