By stalks do you mean the stems coming out of the root? if I can't find the pepper can I subtstitute Thai garlic chili sauce?

Hi barrheadcat, I agree with MirandaR, Thai garlic chili sauce might change the flavor of the dish. A fresh serrano chile would be a good substitute, keeping in mind that bird chiles are really quite small and depending on your heat tolerance maybe you would not want to use the whole serrano. Dried red pepper flakes to taste would also work in a pinch. And yes, for the fennel stalks, I mean the long parts coming out of the bulb. I'd choose the most tender ones, and then remove the fronds. Hope you enjoy this.

I wouldn't use garlic chili sauce just because it's a very distinct flavor. I think that the purpose of the chili here is just a sort of straightforward heat, so I would just look for any little hot chili peppers that you see at the store, maybe ask the person in charge of the produce dept what is the best stand-in chili they have! As for the fennel stalks, you're right! Hope this help!