Are Nature's Life calcium supplements (e.g.,Super Cal-Mag and
Reinforce Bone Formula) good products in terms of the safety of their
calcium source?  I have heard that toxic chemicals like lead can
contaminate calcium from dolomite, bone meal, and oyster shells.  I'd
like to confirm that Nature's Life calciuim comes from safe soures or
is otherwise adequately purified.

Your concerns are justified, and best delt with by using many sources
for your diatary suppliments. This works, as the "natural" suppliment
industry is dominated by small companies. Even where large companies
are involved, the suppliers of ingredients are often small and
multiple sub contractors.
Typically you reduce your risk by taking less than the recomended
amount and/or weekly instead of daily. Most companies take reasonable
precautions, but exquisit precautions are very costly. Our food and
water sources are also suspect, so a wide variety is safest.    Neil