My 01 Expy sags to the pass side a little. I think it would have to be coil spring.
Is there an aftermarket replacement? Checked Moogs site nothing found.

 

Do you have air suspension or regular? Saying coil I imagine you're talking about the front passenger side, not the rear?

 

Std suspension, and yes the rear coils.

 

It's possible that you might have to order the spring by using the spring code from the old spring. Sometimes the code is stamped into the spring and sometimes there is a tag on the spring. If you can find that code, then you can do a search using the code and maybe have better luck.

Of course there's always used parts.
Car-Part.com--Used Auto Parts Market

 

I would replace both sides. If you just replace the left side then the right side will look like it is sagging.