That depends on what exactly you are searching for. A standard reference catalogue for bracteates in German is Frank Berger: Mittelalterliche Brakteaten im Kestner-Museum (Hannover: Kestner Museum 1993). It is available for free download here. There currently is no comparable book in English. A comprehensive discussion of bracteates in English is given by Roger Svensson: Renovatio Monetae: Bracteates and Coinage Policies in Medieval Europe (London: Spink 2013). The book has quite a few weak spots, which are discussed by Marcus Phillips in his review in the Numismatic Chronicle 175 (2015), pp. 389-396 (on JSTOR). Generally, Svensson's book is useful, though. Some of Svensson's research on bracteates is also published in more concise form in Roger Svensson: The Bracteate as Economic Idea and Monetary Instrument, IFN Working Paper No. 973 (2013), available for download here.
Thanks for the extensive reply. This will give me a starting place to do some learning. These coins are not a main line of interest but I am starting to get interested. Carpe diem
