This is a cool idea and while I can't help you with the scans, I do have a few suggestions for you from a printer's perspective who's done some work printing based off of TCG scans before. I used to work in a print shop, and sometimes I would have fun messing around and testing things with various pieces of artwork, including TCG scans.
Definitely get as high a resolution scan as possible, but don't just try and blow up the raw scan without any kind of touch ups or it's going to look very bad. Because the card itself is a printed product (and offset printed, at that) you're going to see remnants from the printing process, and the larger the print compared to the original size of the card, the more noticeable it will be no matter how high-res your scan is. However, if you have a photo-editing program (such as Photoshop or Gimp), you can use various smoothing techniques to remove some of the noise and distortion and clean it up as best as possible. It's still not going to be perfect (blowing up a large, offset printed image never is), but it should improve significantly if you're willing to put a bit of work into it. Using photo-cleaning techniques I've been able to enlarge various bits of TCG art for some purposes, including binder cover inserts and even a canvas banner based off of
one of my most favouritest card arts ever.