I think source code is just a way of tracking your name, address and correlating with your customer history for this store.
Keepsake regularly has discounts of a selected item or line of fabric. Try subscribing to their emails to get notifications on this.
If you place an order online, you might want to do a search for "Keepsake Quilting coupons" before checking out.
I have often found a free shipping code from a promo-code site or blog.