You can read more about the process of refurbishing a leaf spring pack here:
I bought mine through Eaton Detroit spring but I don't see it listed on their website anymore. It's worth calling them to see if they have a line on it still.
The other place I've dealt with in the past for this sort of stuff is Speedway Motors...
http://www.speedwaymotors.com/Leaf-Spri ... ,2079.html
But I don't see 3" listed on their site either. Chances are that they could get some for you though.
I did this to my Jeep and it uses narrower leafs so it wasn't an issue for me to find 2.5" liner but these 3" springs on the van are proving a little harder to track down the right liner size.
On my Jeep it is a totally night and day difference with them in. The leaf springs react so smoothly and progressively... And quietly. I installed them about 5 years ago now and I have well over 200000km on them and the liners are still in great shape. I doubt they will ever wear out. They'll outlast the steel most likely.