On topic: You could probably snoop around DeviantArt and ask artists if you could use their work. Most probably wouldn't mind.
Honestly? I paint my own in Photoshop and/or Manga Studio on a Wacom tablet. I understand that's probably too time-consuming to be practical for most.
Off topic: There's an issue to the wording of that Matt card you have there. Reactions can be revealed multiple times. As you have it worded, any reshuffle allows you to draw your entire deck. Other reaction cards either have actions to prevent such loops (reveal and discard, reveal and set aside) or the effects are such that revealing multiple times is redundant (e.g. Moat, Secret Chamber).
Also, is the Duration one that lasts from play until the end of the game? If yes, it seems like it would be broken especially if you manage to get the majority of them. Maybe the opportunity cost of buying Matt instead of another card is big enough that it's not a big issue, but getting to draw 10 extra cards per reshuffle by ANY player is huge. If no, you should clarify when the card should be discarded from play.
My suggestion is that Matt must be discarded from play in order to draw the extra card.