Yeah, A really good one is the Taylor K-2006 or K-2006C, both from Taylortechnologies.com

Equivalent is the FAS-DPD Service Test Kit from Leslies on-line service.

Search out Chem_geek's recent post--he had a link to the Taylor at a great price. Expect to pay $50-$80 for the kit and it will pay you back 100x over! I have something like 3 versions of it in various forms.