I was going to suggest the fridge, and maybe the freezer, as that's where I tend to put things. You didn't put them back in the seed box, perhaps? Or in a pocket of whatever you were wearing when you sorted them out?
Did you stop to make a cup of tea, and maybe put them in the cupboard with the tea and coffee?
Silly things to ask, I know, but I've done all of these. One thing I can guarantee is that you will definitely find them once it's too late to sow them. I once lost a baby vest that I bought for someone's baby and found it when the child was about ten years old. It had slipped off the shelf in the built in wardrobe and slipped down the side of the old chimney breast that was screened by the doors.