I use the lid to the 5.5 qt casserole on the 9.4" fry pan. You might be able to order the lid thru Sur le Table or Knifemerchant. I don't think Demeyere makes a 12.6" lid. Additionally, there are such things as lids that fit multiple size pans; they have concentric rings in the undersides.
I googled and wayfair.com carries the 9.4" lids. I have never used this company so know nothing about it.
If you can't locate them cheap on eBay, I suggest you call City Kitchens in here Seattle. They carry and stock Demeyere and have tenaciously tracked down things for me. Very knowledgeable staff--what Sur la Table should be. You might try Fante's in Philly, too.