You'd be amazed what some grocery stores will do for you these days, at least around here. Want a product they don't stock, ask and they put it on their shelves, maybe in limited amounts to see if others buy it too.
Pacanis led a discussion a couple years running his PPPC (football) tailgate challenge-- make and serve a food on game day that reflected your team's opponent that week that their city was famous for. PPPC-II. It's baaaack...
I'm sure I had the same dilemma when I made Chicago dogs that you face coming up with some ingredients for what appears to be a simple food--hot dogs.
I think I cheated and used sliced pickled jalapenos instead of sport peppers. I was just looking now, and I see La Preferida is one brand that sells sport peppers. Check the Mexican aisle at your grocery or a Mexican grocery store.
Ditto on the neon green relish. Can't remember if I actually found some or just used a regular relish.
A local grocery sells poppy seed hot dog buns,, so I lucked out there. You might want to check any local bakeries too. Google " how to steam hot dog Buns" there are several easy ways. I don't recommend nuking, as I think it toughens the bread as it cools.
I understand, substituting too many ingredients is not the goal. And it kind of undermines their authenticity.