Sources of calcium for nutritional supplements (bonemeal, dolomite, and fossil oyster shells) all contain lead. Like calcium, lead is a naturally occurring element, and it is cycled through the biosphere as a calcium analogue.

I have actually written articles on this in the past.  The funny thing is that they focus so much on supplements and not the fact that lead is found in most of the plants we consume and is found in high amounts in many things people may not think of such as beard and hair darkening products, garden hoses, artificial grass and even wine:

http://curezone.org/forums/fm.asp?i=1451019#i

They also never question how the lead got in to the supplements.  Most of it came from the years of using leaded gasoline.  The lead deposited in the soil and was washed in to waterways where it was picked up by shellfish.  Plants pick the lead up from the soil where it is consumed by cattle and even humans.  Now think about how many major farms are located right next to freeways where they accumulated tons of lead in the soil from when we used leaded gasoline.  Now think about how much of that lead is being picked up by your produce.  The lead thing has come up off and on over the years from supplement bashers. But I find it interesting that they never test the produce we eat, nor the tissues of animals we consume that eat plants in which lead has deposited.  Just look at how many wine drinkers there are loading up on the lead in the wine.  Where are all the reports about the lead content of wine?  It rarely gets mentioned in the press.

They also leave out the fact that unlike sources such as wine the calcium from calcium supplements happens to displace lead from the body as does silica from plants.

But do you think that the calcium products are tested for high amounts of lead and we can trust manufacturers?

Yes, supplements are actually checked multiple times before they hit the market.  The original supplier supplies a certificate of analysis (COA) to the wholesaler.  The wholesaler has to confirm this with their independent testing to supply their own COA.  The manufacturer often does their own independent analysis to confirm the COA from the wholesaler.  in fact this is mandatory of GMP manufacturers, which is pretty much becoming the norm in the supplement industry.  So in a way there is a lot more stringency with herbs and supplements for safety than there is for pharmaceutical drugs.