Good sources of calcium are green vegetables, in 1 cup raw:

Bok choy:       74mg
Chinese cabbage:74mg
Collards:       30mg
Beet greens:    46mg
swiss chard:    16mg
turnip greens:  105mg
watercress:     53mg
kale:           90mg
parsley:        122mg
mustard:        104mg
Chicory, escarole: don't have figures for those.

other vegetables: 1 cup raw
carrots:        48mg
cabbage:        32mg
sauerkraut:     85mg
summer squash:  36mg
leeks:          73mg
okra:           82mg

nuts 1 cup
almonds:        332mg
brazil:         260mg
hazelnuts:      282mg
pecans:         79mg
sesame seeds:   165mg
tahini(1tbs):   64mg
walnuts:        99mg

sea vegetables:
hijiki(100gm):  1400mg
kelp(1tbs):     156mg
kombu(100gm):   800mg
nori(100gm):    260mg
wakame(100gm):  1300mg
(from Nutrition Almanac by Nutrition Search, 1984)

Weight bearing exercise also helps prevent bone loss by placing controled
stress on the bones. Weight training is a good way of achieving this. So is
walking and hiking. So, eating plenty of green vegetables, some nuts and
seeds, adding sea vegatables to your diet and doing some hiking, walking
and weight training is a good all aound preventive regime.

There are also wild herbs that can be included seasonaly such as nettle
100gm will provide 2900mg, you can also drink it as a tonic tea. Here is a
recipe from Rosemary Gladstar's "Herbal Healing for Women"

Calcium-Plus Tea

2 parts Oatstraw                2 parts Nettle
1 part Alfalfa                  1/2 part shave grass(Horsetail)

Use four to six tablespoons of herbs per quart of water. Place herbs in
cold water and bring to to a simmer over low heat. Remove from heat
imediatly. Keeping pot covered, let mixture infuse for twenty minutes of
longer and strain.

Willow