Finding parts for the JDM B20A is somewhat easy since the engine shares most of it's components with the USDM B20A5. However, the B20A manual transmission is unique and doesn't have any match on other Honda products.
I made a list of ALL the transmission parts with their corresponding part numbers. I labeled the parts that had a direct match with a USDM part number. This means you can go directly to the Honda dealer (or Acura in some cases) and order the parts. This also includes the part number of non available parts so you can order them overseas in you want.
I'm happy to say that every bearing (except 1) are available in North America. I have that particular bearing here and will try to find a match for it in the near future.
Unfortunately, some parts do not have a matching USDM number. However, this doesn't mean another USDM part will not fit. The gears and syncros could be matched with other trannies I'm pretty sure. After all, the D and B series engines share some tranny components even if they do not have the same part numbers.
Here are the exploded view diagrams with a part number list (listed in the same order as torringtonhondaparts.com )
MT CLUTCH HOUSING
MT CLUTCH RELEASE
MT DIFFERENTIAL GEAR
MT SHIFT ARM ROD
MT SHIFT FORK
MT TRANSMISSION HOUSING
I know the diagrams are really big but it's the best way to have the most details you can. If you find them too big, just resize them. These diagrams are not available anywhere else on the internet to my knowlegde so, again, 3geez.com is the pioneer :D. These are the actual B20A Tranny diagrams from Honda.
If you need more diagrams like this on the B20A, let me know and I'll see what I can do.