There are a few in recent years. There's been a Groove Urethane for quite a while, got a basic pancake weight block in it. Likewise the new AMF Black Angle is a pancake urethane ball.
For real cores, the XXL from Lane 1 and black Pure Hammer are discontinued but a thorough search might turn one up on the Internet somewhere. The Slate Blue Gargoyle is more recently discontinued and I don't think it's that hard to find just yet. The XXL and SBG are both pearl urethanes. Hammer also made a Red Pearl Hammer urethane ball until the not-so-distant past, but I think it had a pancake core in it.
Current-line balls, you're looking at the Liberator, Groove Urethane, and Black Angle. In terms of oil-handling, the current Neptune from Rotogrip and Power Groove Dry/R from Brunswick should fill the same slot that a urethane would.
SH