I received a great reply from Prevue Pet (Hendryx) Products. As I originally thought their products are safe and I am happy to continue recommending them/selling their products.
Here's what they had to say.
"I wanted to address your concern about the metal content that Prevue
uses in all of our products, and specifically inside the calcium
perches.
We do NOT use any zinc metals or metal coatings in ANY of our bird
products, including the calcium perches.
The bolt that extends through the center of the calcium perches is cold
steel, coated in a nickel finish. Also, the washer and nut on the end
of the perch is also nickel, and is 100% safe for birds.
Again, we NEVER use zinc or galvanized coatings on any of our bird
products, and we guarantee all of content of our bird product to this
end.
As for the general subject of zinc illness in small birds, there has
been many studies done in the US on this subject, some of them funded by pet associations and the industry. The big problem is that these
legitimate studies are pearls in a sea of poor internet misinformation
and uninformed conjecture. Many vets in the US have been using the
specter of heavy metal poisoning as a blanket statement, when the cause of the illness is truly unknown. They have used "Sherlock holms"
reasoning, in that they can not find the zinc in the food or environment, so they deduce that it "must" be in the cage or toy metal.
This is faulty reasoning, and is not scientifically sound. In fact, studies have shown that poor nutritional balance has caused the body stop releasing zinc from the body, thus causing a build up of natural zinc. It is also easy to forget that zinc is a essential element for bodily function, and vast amounts of it are stored in tissue at all times.
In conclusion, as the subject is very controversial, Prevue goes through
great pains to insure that all of our bird products are free from all
heavy metals (including zinc). We also have all of our products tested
in independent labs to insure and document this fact.
I have to impress upon you again that there is a huge amount of flat out
wrong information on this subject on the internet. This is a product of
our times, when unqualified information can be released under the
premise of an "expert" when this is definitely not the case. I would
highly recommend that you get your hands on a legitimate study ( I would recommend the study done by the University of Tennessee or the
comprehensive study done by the American Pet Products Manufactures
Association) so that your customers can sift through the misinformation
more easily.
Of course I can not speak for any other bird products manufacturer, but
I can state on behalf of Prevue Pet Products, that we are very conscious
of these issues. We have taken the stance that we insure our products
to be free from all of these questionable materials. In reference again
to the calcium perches, we have insured that these products are made
from the "right" materials, but I have seen many competitors who have
not gone thought the research and testing to say the same statement.
There are a lot of bird products out there that are made by companies
whose main emphasis are pets other then birds. By Prevue Pet Products
being highly focused on bird related products, we have a high degree of
focus on bird health related issues, and incorporate this knowledge and
care into all of our products.
I hope that this answers your questions, and invite you to write me back
for follow-up information if you would like. In the meantime, you
should have 100% confidence in recommending our products in the face of these issues. In fact, you should have confidence in recommending
Prevue's products specifically due to these issues!"
I also querried the risks regarding metal rusting and they stated the below which is common sense.
"It is almost impossible to guarantee against rust on metal, not being aware of the environment of use that a product finds itself in. But, if no heavy metals are present in the base product, then a small amount of rust is only iron oxide (iron & oxygen) and is not technically harmful. We do recommend that any rusted cage or toy be replaced, as a point of general cleanliness."
So there you go Prevue Pet & Polly's Perches are safe.