Low pressure check valve supplier

[Travis1]

I’m looking for a place to purchase some check valves. I think I need a Duckbill type valve. I need to attach it to the end of 1/2 inch to 3/4 inch size flexible tubing although the tubing size can be adjusted. The pressure of which the valve opens must be very low. Pressure similar to escaping air if you were deflating an inflatable mattress.

Are there any suppliers that would have such I valve that I could purchase in small quantities? Or is there another type of valve that would work for my application?

I really appreciate any help that you all can provide.

Travis