Hi Hotspur,
I also looked in Domenech's Dagas de Plata, which deals mostly with older gaucho knives and he lists on pg263, under 'brand' Eberle, under `importer' Abramo and under `origin/manufacturer' Brazil, so that, I think, pretty much nails it down.
Of course, the blade or even the whole knife could have been made by various sub-contractors on order by AE&Co, though that we'll probably never know. But... As far as the blade is concerned my mind immediately went to Mundial, a major Brazilian manufacturer of stainless steel knives. The reason I mention this is because there wouldn't be that many manufacturers there with the specialized facilities to make stainless blades as well as other items such as belt buckles, though this is only a guess on my part. In support of this view, I found one early AE&Co gaucho knife, fitted with the famous `Corneta' (Weyesberg) brand blade, so the firm did out-source blades in the past:
http://brasil.abatata.com.br/lista_historicas/456429
Cheers
Chris