So I begin with the usual caveats, i.e. what is magic, what is tradition, what is folk, etc. etc. etc. We got lotsa literature that goes into that in depth, but I'm going to presume that you already know it to get right to what stuff I know is available. Although I also strongly recommend you look into the literature of those questions as a starting point if you don't already know about the essential problems of that question.

I don't know much about the middle or late byzantine traditions, although I can tell you that in early "byzantium," i.e. effectively the late roman empire, we have lots and lots of papyri from Egypt of effectively spells and curse tablets that exist in a grey area between pre-christian and sorta christian. For that there's a great sourcebook out called "Ancient Christian Magic: Coptic Texts of Ritual Power." The book also discusses Christian "Magic" as a continuation of earlier pre-Christian practices, which can be found in "Greek Magical Papyri in Translation." These two books are the best starting sources to talk about "traditions" of magic as they evolved into the early Christian era.

However, we only have this information available about "magical" tradition because they're papyri, and so represent the ritual practices of the average person on the ground. Once you move into Middle Byzantium in Anatolia, the only real document survival you will get will be in semi-officially sanctioned manuscripts which are authorized for recopying. Here you won't get any texts on "magic" (with one exception, Julius Africanus, who wrote a book on secret battle tactics that he didn't think was magic but other people did), but you will get a lot more theological text about argument over the "mystical" experience of Christianity. I mean a prime component of Late Byzantium was the Hesychasm controversy, which was specifically about the role of mystical prayer in the church.

However, I'm far less informed about that subject, but perhaps tracing the origin of Hesychasm through the middle byzantine period would be a start. But then again, you'd be looking at officially sanctioned theological arguments on mysticism, rather than ground level traditions on the subject.

So, I'm going to assume you mean "mystical" in the sense of "magical/supernatural" and not "Christian/monastic ecstatic practices," but let me know if I'm wrong -- the latter sense is much more popular in Byzantine studies, because it's a much more popular subset of studying Christianity, so there's plenty of material to work with on that front too.

In terms of regular old magic stuff -- spells, potions, summoning angels/demons -- here are a couple of sources you might find useful:

• This book is probably the most relevant general compilation of modern scholars writing on Byzantine magic, with a pretty comprehensive overview from Late Antiquity to the 1400s or so. I think you can get all of it from the Wayback Machine link here, but you could also probably get a hard copy through Interlibrary Loan, especially if you have access to any kind of academic library. If you're interested in a specific time period, I'd look for the relevant chapter here and just go diving into the footnotes.
• The Suda On Line is a digitized version of a 10th-century encyclopedia, which has entries both on magic specifically as well as a huge amount of folklore-y anecdotes. Some of these are just quotations from the ancient world, but they usually give some sort of insight on how later Byzantines would have seen them. You can try searching for "magic" directly, or under "religion"/"philosophy" -- it's got a lot of stuff to pore through!
• Somewhat tangentially, you may think about consulting more "religious" than "magical" works, at first, since a lot of Byzantine magic functions through either angels or demons. There's a nineteenth-century translation of Michael Psellos' (11th c. CE) treatise On the Operation of Demons -- very short, written by an incredibly learned scholar who absolutely dabbled with magic himself -- that might be a decent place to start from.

All of these sources are more focused on the Middle/Later Byzantine periods (after about 800 CE), but as /u/bitparity says, there's also a wealth of material available for the Late Antique side of things -- papyri, gems, that sort of thing -- and in any pre-modern period, it's always hard to distinguish "magic" from "religion." But these should at least give you some interesting places to start from.