Hi, this is Steve and thank you for your question on African Violets. Unfortunately, Weld County does not offer a testing service. However, CSU does provide a wide range of tests related to plants, soil and water. Here is the website for that: 
Sample Submittal Forms - Soil Testing Lab 
I know it says Soil Testing Lab, but it does cover all three. I would suggest you call to discuss your INSV issue with them to determine if they can, indeed, test for that. If it proves to not be the case, I suggest you contact the Weld County Horticulture Agent, Jen Rushton <personal data hidden>. She has a Doctorate in Plant Pathology and might have other testing sources. 
Finally, I am sure you are very knowledgeable concerning INSV and here is information from the African Violet Society: 
What-You-Need-to-Know-NOW-About-Impatiens-Necrotic-Spot-Virus.pdf
I hope the above information is useful and you are able to find the answers you seek. 
Please feel free to reach out with any horticultural questions you have.