Some of the ingredients you'll encounter sound terribly exotic and out of reach, but in fact are more than likely available in your town (or, if you're like me, your very New England village in the middle of nowhere). It's worth investigating. Most big grocery stores have "ethnic" sections, and both the Latino and Indian shelves will have a lot of stuff, as well as the regular spice section. The four most basic spices (ground cumin, ground coriander, turmeric, and cumin seeds) are available everywhere. Period.
For the slightly less obvious ingredients, do a Google search for "Asian grocery" or "Indian grocery" in your area -- most likely you'll find one, and it's nice to know that even groceries specializing in East Asian cuisines usually keep most Indian ingredients in stock, too. If you live anywhere near a research university, there will DEFINITELY be a shop like this around, catering to all the science, engineering, and computer profs. Heh heh. A lot of these ingredients will also be available at your local organic or health food store.
When you find the stuff, stock up: spices at Asian/Indian stores tend to be MUCH cheaper than those at your local grocery store, and keep well in the freezer. You can also freeze fresh green and red chillies and curry leaves in ziploc bags to have around when the mood strikes.
Some ingredients may be harder to track down, but don't despair -- the history of Indians cooking in the US and Canada was one of omission and substitution in the years before things became more widely available. My mom almost never had access to curry leaves when we were growing up; she'd make dishes without them, garnishing with cilantro at the end. If there's a dish where no substitution is possible, I'll let you know. Feel free to contact me with questions.
You can also get a lot of the dried spices etc. online. I've had excellent luck with single spices through Penzey's, which is slightly pricey but the products are excellent quality; however, I do find their blends (especially the curry powder and the garam masala) to be sort of weird tasting. Kalyustans, a great store in New York City's "Curry Hill" neighborhood (Lexington Ave, in the 20s), does a quite exhaustive on-line trade of very authentic South Asian ingredients, including pappadoms, chutneys, rices, and even fresh curry leaves. These are only two of many good online sources, keep in mind.
As for what you'll need to keep around: this post gives you an idea of what I think is essential in one's cupboard no matter what cuisines you're interested in. But for a specifically Indian larder, I suggest having the following on hand:
- Ground spices: cumin, coriander, turmeric, red chili powder (note: this is not chili powder as in the stuff you make chile con carne with -- it's ground dried red chilies, straight up), amchoor (dried mango powder), garam masala.
- Whole spices: cumin seeds, brown mustard seeds, fennel seeds, cinnamon sticks, cloves, green cardamom pods, bay leaves, fenugreek seeds, black peppercorns, whole dried red chilies.
- Pulses and grains (I keep the dried versions on hand; you can substitute canned in some cases): chick peas, masoor dal (red lentils), chana dal (also called Bengal gram), toovar dal, besan (chick pea flour), aged Basmati rice.
- Fresh ingredients to keep on hand in the fridge or freezer: garlic, ginger, tomatoes, onions, cilantro, curry leaves, green chilies.
- Other items: tamarind paste (available in concentrate form)
These recipes are written with the idea that you will tweak and adjust according to your taste, but I've tried to be as accurate as possible in my descriptions for the novice cook. Even if they look intimidating, that's only because of the list of spices involved -- if you set them out in advance, the cooking methods are actually super easy.
Most recipes start with some spices bloomed in hot oil, then aromatics sautéed for a while, then spices added, then tomatoes, then braising liquid -- not so different from European methods. Many dal recipes reverse the order: the dal is cooked simply, and then a tadka (a mixture of hot oil, spices, and aromatics) is stirred in at the end.