Here's what I wrote to another mom a few weeks ago who had the same problem:
Oh, you've got a lot to look forward to!
As a near-vegan, I have found that what others consider to be a restricted diet is actually a door to a lot of fun experiments and a whole world of everything else but chickens, pigs, cows, eggs and milk on my plate and in my cup. Since your son is only "restricted" from milk protein, you will have a lot less experimenting to do, but you have every other food on the planet except cow's milk (and foods with it in them) to feed your son. That's a LOT!!
As for calcium, plant-based foods generally provide a more absorbable form, anyhow, so there is no need to worry.
You can find a list of high-calcium foods at http://ag.arizona.edu/maricopa/fcs/bb/highCalciumFds.html (look at the *second* chart; the first one is obviously animal-sourced calcium). You might want to print this chart out and keep it on your fridge till you get really familiar with the great variety of foods you can offer your son.
To introduce new foods, mix some of your choice of his usuals with whatever you're serving him for the first time. He is very, very used to his "comfort" foods, and you don't want to set yourselves both up for food fights and, especially, an aversion to trying new things. I wouldn't worry about this too much. The main thing is to always keep feeding times pleasant and no-pressure. Keep offering him new things - even the same new things - because we all tend to reject flavors that we can't relate in our brains to familiar ones. This is partly why kids say no to new foods. It's a survival trait. We get a taste, our brain says "Whoa, I don't know if this is safe or toxic or what," and we automatically decide we don't like the taste of it. If we try it again after a few days or a week or a year or whatever, our brain then says, "well, I didn't get sick or die the first time, so maybe it's ok...."
For really great ideas, check out Super Baby Food by Ruth Yaron. Here are some ideas off the bat:
oatmeal
papaya
pineapple
kale
collards
Swiss chard!! mmmmm...
avocado
sweet potatoes (Japanese ones are amazing)
barley cereal
millet
apricots
peaches
pears
plums
prunes
brown rice
mango
winter squash
tofu
asparagus
green beans
summer squash
tahini (condiment, say, added to unsweetened soy yogurt)
ground nuts, seeds (condiment)
brewer's yeast (condiment)
watermelon
lentils
split peas
Brussels sprouts
turnips
cauliflower
beets
beans (if canned, drain and thoroughly rinse), mashed or blended to reduce choking hazard
soy yogurt
I got these from Yaron's month-by-month (up to age one). What I have found is, I can just combine pretty much anything with pretty much anything else (assuming it's cooked and soft or blended or ground/blended or soft/chunky or whatever, but of course, not just coined like carrots and not just the way we prepare it for adult meals, at least not till he's used to increasingly thick, etc. consistencies, because that's a choking hazard), and add some of those "condiments" (Yaron calls them "healthy extras"), and even *I* like 'em.
Today, for example, I fed my baby quickly grated, peeled apple, added the juice, and stirred in some tahini and pumpkin seeds (ground up very fine, as all nuts and seeds should be). Took all of 3-5 minutes to pull out the coffee grinder, grind the pumpkin seeds, wash, peel and grate the apple, and stir in tahini.
Other combos: soy yogurt with any fresh fruit, plus ground-up seeds. Any bean in the world (canned is fine) with any grain you like (quinoa is great because it cooks in 15 minutes; amaranth is probably even less). Blend, or mash, and voila. Lunch. Avocado with powdered kelp sprinkled on. Etc.
MAKE SURE TO WAIT FOUR DAYS BEFORE INTRODUCING EACH NEW FOOD. This way, you can observe your son for allergic reactions - anything from a clear, runny nose to an unexplained diaper rash, to more severe reactions (don't worry, severe reactions are very rare when first introduced) - and be sure of which food caused what. This is how I noticed that my baby is allergic to pears.
Baby calls! Good luck!
Ok, later PS now that the baby is back to sleep. By the way, I read the other post, and don't want you to worry about protein. Veg-heavy diets like your son's are commonly believed, mistakenly, to be lacking in protein, or unbalanced (no offense to the other poster. I understand that this is just what we've all been told, all our lives). But it's just a myth. I'm a vegan who has logged intensive hours and hours of research on diet and health, over the past decade, and my mom's an expert nutritionist for the WIC program; I've consulted with her exhaustively on all things food-related, as well. Your son is doing just great. We humans get protein from everything. Just like the animals do. It doesn't have to be combined in any special way, either. Do you know the word for protein deficiency? No? :) That's because it's almost unheard of in the developed world. It's kwashiorkor. As long as a person is getting enough calories, s/he's getting enough protein. And feeding your kid lots of beans is just great. You don't really need them for the protein, but they're healthy and a perfectly good food.