It can be excessively difficult to find good references for Japanese bar money. While I eventually hope my book will eclipse all of the below in terms of thoroughness for this specific series, the best current references that I've found are listed below. They begin with the ones that I've found most helpful. If you're only looking to buy one or two books, start at the top of the list. I'm not including any Japanese sources at this point (aside from the JNDA). They are difficult to find, difficult to translate, and not much use unless you're willing to spend an excessive amount of time translating them. That said, a lot of my information has come from Japanese sources, so don't be alarmed if you find something on this site that isn't covered in any of the sources below. The eventual book will include a full list of references.
Published in 2011, this is the undisputable king of English references. It covers primarily copper coinage, but bar money is also included over the course of two chapters. There is some narrative to explain the history behind the pieces, though it's mainly useful in identifying pieces. It does have some errors and omissions but it exceeds any other English reference by a mile. It's available on Amazon for just $20.
The JNDA is the Japanese equivalent of the Redbook. It lists modern coins in addition to Edo period pieces, including bar money. The values given are way over any market values, but it has color photos for each piece. The catch: It's only in Japanese. There is some English to help you navigate, but you'll mainly be relying on photos and other illustrations. Even so, this is one of the most useful references out there. To purchase a copy, eBay is probably your best bet.
The narrative portion of this book makes little mention of bar money, but it includes a solid bank of photos of the British Museum's collection. There is a free PDF available online, but the resolution of the plates on it is so low that the photos are virtually useless. That said, it's worth a look before deciding to purchase the full book.
This was the first English book published on pre-Meiji Japanese coinage. It was wildly enlightening for the time, but today? Not so much. It was published in 1904 and is now public domain, so you can view a free PDF below. You'll quickly see that it isn't user friendly and the scanned plates are dark and unclear. If you were able to find an original copy with good plates it would be a nice addition to a collection, though still not overly helpful as a reference.
This book was originally released in 1953 and eclipsed Munro at the time. While it was an improvement, it's also fairly light on illustrations with no information that isn't included in Hartill (though it does contain more inaccuracies). If you're going for a complete library then this is an important stepping stone between Munro and Hartill, but if you're looking for reliable information, look elsewhere.
Jacobs did have a noteworthy collection of bar money which was sold by Heritage in 2011. For some of the rarer types those remain the only US auction records in recent memory, which are more useful than the book itself.
You'll notice that all of the sources above are very specialized. There's a reason for that; generic sources just don't do this series justice. If you're just looking for information on bar money, don't seek out a Krause catalogue or wide-reaching book on coins of the world like Craig or Friedburg. We may use their numbering systems, but you won't learn much from them. If you have one on hand, feel free to look them up, but don't seek them out specifically for this series. You will be disappointed.