Malaysian dessert places are more difficult to find in LA than in NY, where Penang restaurant originates from. But you will find very close Taiwanese, Vietnamese, and Korean approximations, often in buffet style, in a number of locations.
For Orange County, your best bets are
1) A number of Vietnamese restaurants / shave ice places in the city of Westminster, including Uyen Thy Quan (9600 Bolsa Ave), which is open 24/7.
2) Shau May, the chain of Taiwanese shave ice places, has many locations, and I've definitely seen one in Irvine.
For Malaysian food in LA County, the best place is Little Malaysia, on Peck Ave in El Monte. I also believe that Singapore Express, at Lincoln and Maxella in Marina Del Rey, has ice kachang.
I'm not sure if its the same thing, but I buy a syrupy rose water (and other interesting syrups) when I cook Middle Eastern. In the South Bay, there are a number of Middle Eastern grocery stores that carry it -- most notably is Rio's on the corner of Mackey and Artesia in Redondo.