Here is a list that should answer many of those questions.
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Acetaminophen generic Tylenol, grocery store/drugstore
Acetylsalicylic acid - aspirin, grocery store/drugstore (may require purification from binders and fillers for some purposes)
Acetic acid, dilute available as vinegar at grocery stores. Buy the cheapest white vinegar you can find; you don't want the flavorful organic traces of the more costly brands.
Acetic acid, glacial (concentrated) photo chemical
Acetone available as a solvent in paint stores/aisles and as an art supply.
Aluminum, foil - pretty obvious, at the grocery store. Be aware that most foil will not be pure aluminum but will contain small amounts of other elements such as silicon and iron.
Aluminum, powder - available as a filler for certain mixtures used with fiberglass; found at fiberglass suppliers (you may want to look online). The powder may come coated with some waxes or oils; these can generally be removed with cautious heating in an oven (BEWARE: aluminum powder is a flammable solid that burns with great heat once ignited) or rinsing with acetone.
Ammonium bifluoride, solution - hardware stores, as toilet bowl cleaner/rust stain remover
Ammonium hydroxide, dilute this is clear household ammonia. Beware, you don't want perfumed, colored, cloudy, or sudsy ammonia. Before buying, pick up the bottle and shake it. If it forms suds, you don't want it. I found plain, clear ammonium hydroxide at the local Thriftway as "Western Family Clear Ammonia."
Ammonium hydroxide, concentrated you can purchase a far stronger ammonia solution as a blueprint supply; search online (I've never seen a local blueprint supply store). This is not as concentrated as ammonia can get in water, but it is quite strong.
Ammonium nitrate available as prills at larger agricultural centers, in large sacks. You probably don't want to buy so much. Besides which the salespeople may be suspicious, since ammonium nitrate is easily converted to a blasting-grade explosive. More manageable amounts of ammonium nitrate (at much higher unit prices) can be found inside of instant chemical cold packs found in pharmacies/health aid aisles. Carefully cut open the outer plastic bag without puncturing the water bladder within, and store the pellets in an airtight container, since it is quite hygroscopic (absorbs moisture from the air).
Ammonium persulfate used to etch printed circuit boards; electronics store (catering to professionals; not Circuit City) or online
Ammonium phosphate available as a fertilizer, from agricultural/garden centers. I have actually seen this in chain stores too. Of course, you're once again stuck with a large container.
Ammonium sulfate another fertilizer that may not be too difficult to find.
Borax see sodium borate
Boric acid available from drugstore; I found mine at Bi-Mart.
Calcium chloride may be sold as a granular de-icing mixture at hardware stores; also sold as moisture absorbant in smaller containers.
Calcium carbonate chalk, marble, limestone - find these and you've found calcium carbonate.
Calcium hydroxide hardware store, garden supply center; may be called "lime," "hydrated lime," "slaked lime."
Calcium hypochlorite "shock treatment" chlorinating agent for pools. The purity varies considerably according to brand (examine the label). The purest materials may be hard to find outside of a dedicated pool/spa center.
Calcium nitrate a fertilizer - again, one that you're not likely to find at the local Target.
Calcium phosphate fertilizer
Calcium sulfate zounds, another fertilizer