Signs MT is a font with the card images in it. Search for Signs MT at Eyewire or Adobe and you should be able to find it. Since these are font images, they'll be a single color outline but you may be able to type them in the size you want in Photoshop in Black, render them, then color them in.
Also, did you check the web sites for Visa and the rest? I'd think they'd have downloadable GIFs on their site. (If they don't, they should -- all those blurry Visa cards aren't doing their brand image any good.)