What do the sizes of sm-xxl correspond to in waist size in inches (e.g. 36")?

XL worked for a 36 inch waist. Depends how you like your fit. Also underwear as a whole a little roomier.

I bought the xl. my waist is 39 and they fit fine. however, they're made of 100% cotton. should i have bought the 2xl?

I'm guessing you are concerned about shrinkage. Check the fit after wash. And as always, colors in cold.

do these underwear comes in sizes 30 to 32

Soooo.... My experience with Tommy Hilfiger briefs is that they come in S, M, L, XL! I Wear a size 33-34" pants, shorts, etc. Normally that would correlate to a " M", however, I always buy size " L" since, by nature and being cotton, they do shrink. So after a couple of washings and drying they shrink down one size and give me a firm fit at around a 32-33 waist size. Tommy Hilfiger briefs are the only ones I will wear. Durable, comfortable and a nice snug, supporting fit!

Country manufactured in?

The packaging from my purchase about 7-8 months ago now shows that they were made in Sri Lanka! And not that you asked but... The quality is what I've come to expect for these briefs. They've been my choice for probably 20 years now.