There's not too many others with the same kind of sign up bonus value outside of Chase. Mostly you'll be finding $200-300 bonuses, it was a sad day when they pulled that application.
If you haven't looked through already, DoC has been keeping a list of good sign ups to read through -
https://www.doctorofcredit.com/best-current-credit-card-sign-bonuses
Could spark another idea. But with lower value bonuses, you'll need more cards to make the same amount which could change future sign up plans. Depending on how much you still need to cover, have you looked into bank bonuses for some cash too? Things like the Wells Fargo CC offer DoC mentioned that can only be applied in branch would be a good time to double up with a new account opening bonus. Between the two that could generate $600-800 dollars towards tickets ( depending on the current WF offers out)
May have to take some time to generate a new strategy since I'm not sure there's a single card that would be as easy to substitute. Unless you took a Chase offer and cashed out the points - but from other replies I gathered maybe Chase isn't a good fit if you want this card for DH. (Sorry if I missed anything, I'm mostly skimming the last few days)