Man, I was just browsing for 'The Invincible Legend' merch last week, and let me tell you, it's a bit of a treasure hunt! Official stores like the publisher's website or big retailers like AmiAmi and Crunchyroll sometimes stock limited runs, but they sell out FAST. I snagged a cool hoodie from their collab with Uniqlo last year, but you gotta follow their social media for drops—no joke, it's like concert tickets.
For secondhand gems, I swear by Mercari Japan (proxy services like Buyee help) or Mandarake. Saw a rare acrylic stand from a 2018 event there last month! Just watch out for bootlegs on shady sites; if the price seems too good, it probably is. My rule? Reverse-image search listings to spot fakes.