There are not too many books about ‘our subject’. What is more, when you can read only English, there is even less to read.
The Early History and Antiquities of Freemasonry: As Connected with Ancient Norse Guilds, and the Oriental and Mediæval Building Fraternities by George F. Fort (1809-1872) (published 1884) is not only the classic book, but also one of the few books available in the English language. Some quotes from the book can be found here. The book is not very good, but has a lot of leads and interesting approaches. Better books have been written later, but for English speaking readers, this is a must-read.
99 Degrees Of Freemasonry by Henning Andreas Klövekorn (1975-) is only partly about ‘our subject’. The chapter that is of most interest, can be read online as well. Klövekorn’s ‘route’ is mostly continental European as he focusses on German Masonic guilds of the Middle Ages. Here we have a living and writing Freemason, Asatruar and more.
That is all I know that is available in English. The most interesting works are written in Dutch.
Noordeuropese Mysteriën En Hun Sporen Tot Heden by Franz Eduard Farwerck (1889-1969) is a classic in Dutch. 760 Pages with a long line between rock carvings and modern Freemasonry. The book is fairly well available second hand. In other (less easily to find) books he also writes about the subject, mostly Noord Europa, een der bronnen van de Maçonnieke Symboliek (1955). Much more about Farwerck at Farwerck.nl.
Thriving on Fort, Farwerck and Grimm (see below), but with tons of extra information is From Times Immemorial… de miskende wortels van de Vrijmetselarij (2010) by Koenraad Logghe (1963-). This book poses an extra problem. It is self-published (small edition), only available from the author and only for regular Freemasons. Eight years after its publication second hand copies fortunately are available every now and then. Logghe gathers all available information and adds a lot of his own. He is another living Freemason and Asatruar. The book is massive, 500+ pages on A4 format.
A book that Logghe refers to and Fort to a lesser extent is Deutsche Rechtsaltertümer (1828) by Jacob Ludwig Karl Grimm (1785-1863). This book is not about the Northern European origins of Masonic symbolism, but about “German legal antiquities” which prove to have a lot in common with some Masonic usages. The book seems to be only available in German.
Arvid Ystad published his Frimurerne i Vikingtiden in 2016. As the title suggests (‘Freemasonry in Viking times’), Ystad found Masonic symbolism among the Vikings. His book is quite extensive, does not use (m)any of the sources above and is so far (late 2019) only available in Norwegian. The author is working on an English version.