After a bit of googling, it looks like coffee grounds are close to neutral pH, so I wouldn't worry about acidity there.
If you have too much "browns" and not enough "greens", you could take a different approach: instead of adding your dead leaves to the compost pile, make a dedicated leaf mold pile. This will take a long time (up to two years) to break down, but when it does it makes a nice low-fertility soil amendment. No need to worry about acidity here either: leaves are acidic, but the end product from your leaf mold pile will have nearly neutral pH.
As an aside, do you have a constant stream of wood shavings that you're adding to your compost pile? If so, have you considered other ways that you might use these around your yard, e.g. as mulch? I only ask for the same reason I suggest the leaf mold pile -- using the shavings in some other way could help you balance your compost pile better.
Now, on to the answer to the question you posed... sources of greens (high nitrogen):
- kitchen scraps
- coffee grounds
- lawn clippings
- fresh weeds
- animal manure
- apple pomace
- human hair
- hops (brewery waste)
- a number of other sources of vegetable waste
As for places to acquire these ingredients:
- As you mention, you can get coffee grounds from work or from a coffee shop.
- You could try making arrangements with the cafeteria at work or a local restaurant to use their kitchen scraps. (But I'd guess that they'd want a commitment from you to haul everything away, which could be more than you can use. Depending on how careful they are, you may get some contamination with stuff you can't or don't want to compost, e.g. meat, dairy, trash.)
- You can ask for veg waste from the produce department at your local supermarket.
- Ask your neighbors if you can take their lawn clippings from their untreated lawns. You don't want to import herbicides into your compost!
- If there are any kind of fruit/vegetable processing plants locally, they may have waste products that you could get for free.
- Ask for a bag or two of hair from your local barbershop. (According to "The Rodale Book of Composting" on p93, 6 pounds of hair has as much nitrogen as 100 pounds of manure.) Make sure to mix well with your leaves/shavings because hair mats down easily.
- If you have a local brewery, ask if they'll let you take away a few buckets of their waste. Hops or grain mash are both good additions to the compost pile. If they're soggy, make sure you layer well with your dry leaves and shavings.
- If there are any farms in your area, or people with backyard horses or chickens, you may be able to get manure free for the hauling.
- Beware that horse stall bedding that includes wood products (shavings or sawdust) will behave more like a brown (or neutral) than a green.
- Beware that manure from horses will contain a lot of weed seeds.
- Beware that hay as a bedding material will contain a lot of weed seeds.
- Beware that manure from commercial feedlot operations may contain high levels of salts.
- Even with all of these caveats, I'm a big fan of manure in the compost pile, mainly because for me it's home grown, easy, and free.
- You can grow a "compost crop":
- Comfrey is a perennial with leaves that can be harvested multiple times a year and added to your compost pile.
- Various annual/biennial cover crops make a nice addition to the compost pile: buckwheat, clover, small grains like oats (if you cut them while they're green -- before they become mature, toughen, and turn into straw which is high carbon).