Akihabara is just convenient. When I lived in Koshigaya, the train went straight to Akihabara. And now that I live in Funabashi, I can go straight to Akihabara just a little faster and cheaper! So throughout the year, it's usually my first stop when I go into the city. And my first stop once I get to Akihabara is usually the Yellow Submarine/Mint trading card shop located just outside the JR train station.
It's not a go-to place for set builders or those looking for some high-end singles, but if you want the latest BBM set singles, this is a good bet. In addition to a pretty good stock of the newest packs, boxes, and box sets (both NPB and MLB), they have a decent selection of singles from the pack-based Japanese releases. Space is limited here, though - a small section of the shop is shared with idol, soccer, and wrestling cards. So about once a year they go through and clearance some of the numbered parallels from their display cases.
Deals aren't necessarily tremendous, but I enjoy this event because I can usually clean up pretty well.
I usually pick up a few autographs, too. There weren't many offerings this year.
That's this year's haul. However, finding fun clearance cards isn't limited to just once a year. I've found good deals in the display cases before, and occasionally people sell cards to the shop and those get put out either as singles or lots. I recently found a bunch of Bikkuriman stickers I needed for my sets, and they usually have a handful of vintage Calbee singles to go with the current releases.