I think this is due to the fact that as a hunting weapon market, Belgium was negligible.
The vast majority of the stuff was exported to France, US and Germany.
At least that's what the forensics say.
In that context, there would be almost no point in publishing anything locally, as there would be no customers to convince and therefore no advertisement money.

Of course, whatever was in Belgium in 1940 went to Germany anyways, and then on to the US in 1945, so maybe I am wrong, but if you look at the country size, density, etc., I still think I am about right.
Best regards,
WC-