I’m sorry you’re having difficulty finding a place to have your soil tested. 
Soil testing and following the recommendations given will definitely help improve your chances of success in growing dahlias. 

My online search indicated that the Lucas County Soil and Water District provides help with soil testing. 

https://www.lucasswcd.org/

Below is a link to an Ohio State University fact sheet on soil testing.

https://cfaes.osu.edu/fact-sheet/soil-testing-horticultural-needs

The factsheet contains information on how to collect soil samples. Near the end of the factsheet is a list of labs that perform soil testing. You can request soil test kits from the lab of your choice online or by phone. Each lab should have instructions on how to send the sample(s) in for testing. Be sure to indicate that you will be growing dahlias. 

It’s best to allow the soil samples to dry out, as indicated in the factsheet, before submission. Soil testing you may want to collect the sample while waiting for the test kits to arrive.

You might want to contact the Lucas County Master Gardener volunteers. They should be able to give some assistance 

The OSU Extension Lucas County Master Gardener Volunteers program, based at the Toledo Botanical Garden (5403 Elmer Drive, Toledo, OH),  Contact & Location Details

• Office Location: OSU at Toledo Botanical Garden, 5403 Elmer Drive, Toledo, OH 43615 (Off Elmer Drive; office located between the Rose Garden and the Inclusive Garden).
• Phone: <personal data hidden>
• Email: <personal data hidden>
• 
  Should you require further assistance please reply to this answer.