A quick peek at the LVA "best video poker" listing shows that Bellagio, Excalibur, Luxor, MGM Grand, Mirage, Riviera, and TI have 9/6 Double Double Bonus Poker. You may have to look at vpfree2.com to find the machines' locations or to even see if the machines are still there. Riviera has quarter 9/6 DDBP and above; all the others listed are $1 and above denominations.
If you are willing to stray from the Strip a bit, Palace Station and Palms have optimum-play 10/6 DDBP.