Man, tracking down band merch can be such a hunt sometimes! For 'His Hero Is Gone' tees, I'd start by checking specialized punk/hardcore online stores like Angry Young and Poor or No Echo. They often carry underground band gear. Etsy or Depop might have vintage finds if you dig deep—I snagged a rare 'Monuments to Thieves' print there last year. Also, follow HHIG fan pages on socials; sometimes members sell old stock or bootlegs pop up (though support official drops when possible!).
If you're into screen-printed stuff, indie distros like Toxic State Records or DIY bands' Bandcamp pages occasionally restock. The key is patience—this isn't mainstream merch that stays available forever. I missed out on their 2017 reunion shirt and still kick myself!