The HACH Company website
http://www.hach.com/
To contact the HACH company if you have any problems is to go to their Contact us section of their website and they give multiple ways on how to contact them.

Other companies that may carry the supplies needed

The Lamotte Company can also be used to purchase products however they do not have the option of buying online but they do give you locations where their products are sold
http://www.lamotte.com/index.html

The Carolina Biological Company also carries the supplies that you would need and they do allow for purchase online.
www.carolina.com