Hey, does it have to be attached to the gain? Here's an idea:
Farmerinthedelle$4 - Action
Take two coin tokens. This turn, when you spend a coin token, reveal two cards from the Black Market deck. At the end of your turn, shuffle the revealed Black Market cards and put them on the bottom of the Black Market deck.
In games using this, revealed Black Market cards are part of the Supply during your Buy phase.
(Before the game, make a Black Market deck out of one copy of each Kingdom card not in the supply.)Only one line is needed; the BM setup text is actually a small parenthetical.
I made it on play like Bridge to save an extra line. I think the combo with e.g. King's Court is fine.
This card differentiates itself from BM in a few ways. You lose out on pseudo +Buy, but you get coin tokens and can potentially dig a bit further through the BM deck. If you just spend both coin tokens immediately, you get to see 4 cards instead of 3. They also stack when you play multiples, so you can reveal even more. I made the card return "shuffle" instead of "any order" just to prevent a lot of potential AP if you have to order a dozen cards.
You lose out on tricks with playing treasures in the action phase and potentially drawing and playing the new card, but you gain some tricks that come from treating the cards as part of the Supply. For example, you could gain them with HoP, Border Village, Farmland, Ball.
Random clarifications -- I think it should also trigger when you pay coins to Butcher (which also opens up the possibility of getting BM cards through gainers like Ironworks).