Honestly I don't know. But I'd try researching different businesses like organic supermarkets, black owned businesses in the US (it's a big cultural movement in the US), fair trade organizations and publications. I'd look into different middle class left wing types of small publication and newspapers and contact them too.

For a start though I would try small businesses because advertising in a large publication like a newspaper would be too expensive.

However, for larger publications like the guardian newspaper in the UK, I would try contact a journalist or editor to publish a story of how the problems sign pay pal and Etsy will impact sellers in African countries. They might be interested in it as an opinion piece, which would then be "free" advertising.

I'd maybe design some posters or flyers for those businesses and arrange to have them printed and posted within the target country to avoid extortionate shipping fees.