Darice Self-Sealing Bags 4 1/8 x 6 1/8 make great alternative sleeves. You can trim them or fold it back and seal the cards.
www.darice.com/store/details/catalog/wholesale-basics-organizers-storage-poly-bags/1115-14
Character Card Sleeve Alternative
The ones from Thailand are perfect size. Awesome. Another one I like is the 4x6 photo sleeves.
DomaGB, yes they are. I just wanted to point these out as a readily available and cost effective solution. I've used the photo sleeves as well. It is worth noting that even those these are long, height wise (the 4 1/8) is a nice snug fit. Again the length is easy to trim or to simply fold back and seal the card (this has saved a couple of our character cards from spills already).
I'm afraid the Thai making those neat sleaves hasn't been active since 5/2014. What other alternatives are there at the moment?
Check out the latest entry (at the bottom) here -