It will be way less expensive to stick with what you got. In your area there is likely a suspension shop that has a contact for leaf springs. I used to work at one where we built our own spring packs as per manufacturer spec. There may be one of those shops in the area. Ask around, look in yellow pages and I bet you can get help without going to the dealer. Why is it that you have been told you need new leaf springs? Broken or sagged or what?
If none were broken then could add a leaf on each side and rearch but if try that then will have one leaf newer on one side so recommend taking to a suspension shop for help, they can order in new sets and give you price first before any work done.