If you want access to Vietnamese sources, you may have to learn both "chu Han" (classical Chinese, used in formal documents like court history, royal eddict, legal and administrative document...) and "chu Nom" (logographic writing system of Vietnamese language, used mostly in literature).

Nowaday, some universities offer a bachelor course on Han-Nom. There are some smaller course provided by individual teacher as well. If you don't speak Vietnamese or Chinese, then we are talking about learning 2 new languages, both are quite difficult.

A good source that lists all the alternative characters can be found over at the Nôm Foundation website. I've personally used this tool to help me learn Nôm myself.

#祝伴𢆧𪪉!