It's very hard to buy doujinshi outside of Japan. Some events in the US have people who buy them from Japan and re-sell, and there are a few place to buy online, but mostly it is very hard. Personally, I don't live in the US, which makes it even harder, but I did get a friend to buy some yoshitoshi ABe books for me.
Untranslated manga is not very popular, and only really big fans will usually buy them. Of coures, with ero doujinshi you don't really need to understand the text, so those are a bit more popular.