@pichufan @zacheggers Ok, I never expected I would say this to a question like this, but: I’m unable to find any that you haven’t found already… 
I looked at all my regular sources first. The ones I could find were already in your list. At first I thought two were missing, but one actually has Pichu in the name (the Pikachu & Pichus Jumbo), and the other turned out to be a Pikachu (one of the other Illustrator Zoruas).
I then looked at all my Pikachu cards and Jumbo cards. Still none you hadn’t already found.
Then I looked at ALL my 5k+ cards. And let me say, I found loads of Pokémon hidden in the background I didn’t even knew about… Like five cards with a tiny Pikachu I didn’t knew I had, some Plusles and Minuns playing in the background, and loads of Pokémon you wouldn’t expect in the back of other cards like Tauros, Exeggutor, Mienshao, Sandshrew, Vanillite, Mr. Mime, Jumpluff, etc. etc.
BUT, I couldn’t find a single Pichu that wasn’t already in your list… I got excited a few times when I found one, only to check your list and see it was already there. Maybe there are still some out there, but I must say I’m very impressed (and frustrated 
) by the list you’ve already compiled yourself.
Greetz,
Quuador