Are there any "premium" cards available for purchase?
Nope, none that I know of unless you count the ones in the Lance Packs and I do not consider them premium. The edges are mess from bad die cutting. They are not laminated so you can use a white board marker for scoring and they are small. I also do not like that they are double sided. I would like the cards to be larger as well.
I am in the process of making my own cards. I almost have my Photoshop layout complete.
I am making them 3x5 with my own Alpha Strike Graphic in the back. I am sticking them together with a thick 3x5 card in the middle to make them thick. Then I am going to heat laminate them so I can use a dry eraser pen marker.