It's hard to find brands like Gregg Homme, Joe Snyder, etc. You can find Andrew Christian, and you can find off-brands, but it's not what it was even five years ago sadly.
I think Nasty Pig is still open, but does not carry other brands of thongs. While shopping online is good, buying over the counter is a great experience (as well as using the change room to try on and check fit :-)!).
I just found out about a place called Pure Seduction right next to the movie theater on 6th/W4th that carries a ton of thongs from German brands I've been looking for for a while (mostly Manstore and Bruno Banani). Legitimately first store on years in NYC to have more than a few thongs, and they're pretty good design wise.
Apparently they've been open four months, haha. No clue how I missed them, I eat ramen nearby all the time. Welp.