I found card protectors that are the right size for Dust unit data cards in my local arts and crafts shop. They are clear plastic sleeves, 15 x 10 cm. I found them with the ziplock bags and similar items. I think that people use them to store small bits and pieces, or package things they have made (for sale at markets or whatever).
15 x 10cm is almost an exact fit for the Dust cards. Actually, a very tight fit, because I had to bend each card slightly to slide it into the sleeve. (They have flattend out, since then!) Now, I do believe that Dust sell card protectors on their website, and those ones are probably more hard wearing than these, probably like the card protectors people use for Magic and other games. But, the main feature of the ones I use are price: $2 for a pack of 10. Bargain!