Oyin handmade sells sample sizes: Oyin Handmade: Nutritious and Delicious Care On The Go!
Jessicurl provides free samples with orders: Samples-Shop Now
but you might contact them and explain your situation. Maybe they would be willing to make some arrangements with you, since it could bring them new customers.
Komaza Care also has samples sizes: Samples-Shop Now
Curl Junkie sells sample product sets: Trial / Sample Size set and Sales! | Curly Hair Products | Naturally Beautiful Curls | Curl Junkie | Addicted to Curls!
There are probably others, but these are the ones I know off the top of my head. HTH!