Shader on 3D model not seen over 2D sprites

Hello!!

I have a question about shader coding.
I'm only begginer in this thing, so anyone can tell me is it possible to 3D models with alpha shders to be seen over 2D sprites?
Example:
There is a sphere on scene and beyond it some sprites
while in sphere shader setting are
**#pragma surface surf Lambert**
it seen ok:

but I need it to bet transparent, so i change shader to
**#pragma surface surf Lambert alpha** and then I got this:

my sphere is visible only over free space. Looks like it rendering behind all sprites now.
Is there a way to render it as it does on first pic, but with alpha transparency on?

Shader is included. Alpha on line 22-23