This is my favorite game and I continually hunt around for it at the casinos. Here is what I've found:
Riviera: 2 $.25 9/6/4 machines in a bank of uprights near the bar
Lady Luck: almost all the flat tops in the lower level near the poker room are $.25 9/6/4 ddb
Lodge: a bank of flat tops near the north bar are $.50 and $1.00 9/6/4 ddb
Canyon: 2 $.05 9/6/4 ddb uprights across from the players club and 3-4 $.25 9/6/4 ddb at the bar
Fortune Valley: a double bank of $.25 9/6/4 flat tops at the east end of the upstairs area and a couple banks of $.25 9/6/4 uprights at the west end of the upstairs area
Century: all the machines at the bar on the lower level are now 10/6/4 ddb for $.25! They comply with Colorado's ban on 100% plus games by only paying 40x on a straight flush. They claim the payback on these machines is 99.95%.
Also note that Bullwhackers has progressive $.25 9/7/5 DB on uprights in the Big Deal VP room and Fitzgeralds has $.25 9/7/5 DB on uprights in its upstairs VP area near the windows.
Happy gambling!