One of the easiest ways to find backlinks is to use SEO tools and profile your competitors.
You mentioned that you are targeting the Bulgarian and Spanish markets.
Look for your competitors in the Bulgarian language, as well as in Spanish.
Where are they getting their links from?
Do those place allow for guest posts?
Can you get contact info from those places and possibly get a deal going?
Believe it or not, a lot of websites that link to other sites will actually take your money for a link placement.
You just have to approach them the right way—don’t straight up ask them, “hey, do you sell links?”
In many cases, they would say that they take guest posts but they have to charge some sort of “processing fee.”