I tried to come up with a promo that would specifically work well with Scout. It wants to cost $3 so you can open X/Scout and people don't just spend all game wishing they had access to Cartographer instead. Something like:
Prospector
Action - $3
You may discard any number of Victory cards from your hand. For each one you discard, +$1.
Reveal the top four cards of your deck. If none of them are Victory cards, gain two Silvers. Discard the cards revealed.
Trouble with this is that it's fantastic if you manage to collide your Scout and Prospector, and terrible if you don't, like opening TR/Swindler. Maybe something that lets you trash it for a card that costs $4 so you can gain Scouts with it when you need them without having to find the +Buy in some later turn?