To find someone to test your product, just do what you did here...make a post. Say that you are looking for beta testers,  the item you want beta tested (if it's a clothing texture make sure you mention that they need to have the original clothing), if it's a skin texture/character package mention the figure it's for.  And what version of Poser and/or Daz|Studio you want it tested in.

I don't do the creative end of things so I don't know how many beta testers most people get for each version they want tested.  For me if I were to need something beta tested I think I would go with 2 people per each version because someone might take on the task and not finish it and this way there is someone else. 

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi