D76 is the best way to do B&W for a beginner, very handy and reliable. Try B&H or Adorama for chemicals (I am not in NYC but they are the big camera stores there).
Do you mean commercially-packaged photochemicals (D-76, XTOL, Rodinal, etc.) or raw ingredients (metol, phenidone, sodium sulfite, etc.)?
For the former, B&H and Dead Link Removed are both close to you, in New York City, and Freestyle is further away in California, but still potentially useful. There are others, too, of course, but those are the "big three" in my mind.
For raw chemicals, Photographer's Formulary is probably the best-stocked option, but their Web site is down at the moment. Art Craft and Digital Truth are a couple more with decent selections. B&H sells some raw chemicals, too, mostly from Photographer's Formulary. Various other sources, such as The Chemistry Store, sell some useful chemicals, but lack some of the items that are necessary for photography but uncommon for other uses, such as metol and phenidone. There's also no guarantee that they won't contain contaminants that might be detrimental for photochemical purposes.
D-76 is a very popular general-purpose developer, so it's a good way to get started, but certainly not the only way. Others include ID-11 (Ilford's version of D-76), XTOL, and HC-110. It's hard to go badly wrong unless you get into very exotic developers, such as those for producing very high contrast or for developing in very high or very low temperatures.
If you are interested in raw chemicals, techcheminc.com is complementary to thechemistrystore.com and the prices are reasonable. They sell developing agents, benzotriazole. etc.
So the perfect way to understand what You exactly need from darkroom
is buying "ready to using" (i.e. pre-packed, commercial, etc.) solutions
from B&H (in most cases expensive place for B&W photographers),
Adorama.com (less expensive) or DigitalTruth.com (wide range of
chemistry).
And also great to be sticky to one or two film-developer pair
to obtain better knowledge about that exactly happened in Your
darkroom.
After some time (6 month i hope if You are shooting regularly) You
know what You exactly need from film, know about George Post
and his "Shake It Up" article in Darkroom Photography about
"best" agitation methods, and what is strange "TAS Processor"
words mean and why that small electro-mechanical tool cost EUR 845.00 (around $1,082.00)
(link to manufacturer's Heiland Electronic web) opposite great $29.00 AP tank.
If You have perfect iPhone / iPad from Apple, You may
enjoy very useful app named "RAW Chemicals for Photographers
Darkroom". This app have index book about raw chemicals, chemicals store finder
with Google map navigation (great in a car) and feature to sending
email request with selected chemicals to stores.
Other great app for real "analogue" photographers You may
find at Black&White Photostore page on AppStore
and more are coming in August and September.
Keep in touch.
p.s. Most of European / Germany photographer's
chemicals stores have a REALLY WIDE RANGE
of chemicals for darkroom that You may not find
or very expensive in USA. Just go and try...
In past time more and more really BIG stores with huge number
of local representatives like CALUMET, B&H, Amazon like to totally
switch to digital due reducing payments for buying analogue film,
papers, chemicals, cameras, etc.. and pay for great specialist in this
area.
Digital are less expensive in support (HUGE number of models,
well described in internet, no needed special expensive approving
for storing hazard in most cases chemicals...). And give a HUGE
profit.
And economical recession speed up this process. Just read this forum
how B&H "experts" answering about b&w film availability....