Model of belt used in john deere d140 models: gx21833
as product features;
Specification Belt Section HA Effective Length 141.709 IN Width 0.559 IN Thickness 0.449 IN Angle 38 Material Spec ARAMID
the price of this product ranges from $ 30- $ 40. you can easily find it on Amazon.
if it is not suitable for you, you can look at other belt models.