You could get a set of 2500 leafs from a junk yard unless they are beat springs usally last along time. As for the 2500 vs 1500 the 2500 usally have a lower gear ratio which gives more power but less millage check the millage thread to see the difference.

 

Eaton Spring can make just about any spring configuration you can think of. I think they're at Eatonspring.com, but I'm not positive about that. They make springs for manufacturers, and claim to have files on just about every vehicle ever made. They have a price list on their site also.