I'm having a greek dinner party and wondering if you can recommend a grocery store that carries greek specialty foods.
Titan Foods in Astoria; International on 9th Avenue and 40th street in Manhattan. Not sure what you mean by groceries, though...do you mean fresh produce? Spices? Cheeses? Ready-made things?
I'm Greek-American and throw a greek picnic for my friends every summer. I always make a pilgrimage to Titan Foods in Astoria (their olive and greek cheese selection alone are with worth the trip), but it can be a bit intimadating if you don't really know exactly what you are looking for. Nearby are also greek-owned liquor stores where you can find better selection of greek wines than you can find in Manhattan. In Manhattan, International on 9th is much smaller, but also good-- many consider their pre-made taramasalata to be the best in the city. Close by on 9th Ave is the Poseiden Bakery which carries many traditional Greek pastries and cookies as well as their own homemade filo dough. I also love Kalustyan's on Lexington and 28th Street which is not exclusively greek, but carries many greek specialty products or their middle eastern equivalents. All the greek dried herbs are there as well as sage tea, filo, rose water, greek cheese, excellent dolmades, halva, baklava etc. Finally, the Westside Market on 7th Avenue at 15th St is Greek-owned, so they have a surprisingly deep selection of greek cheese. If you have a more specific question about what you plan to make, feel free to ask. Good luck!
If those stores have bulgarian feta, I'd urge you to try it, your guests will apprec the difference.