I guess I should have looked at the schematics before posting that comment 
, because it turns out the opamp is only used to buffer the filtered dual PWM output, so if you have ±12 V you can power the opamp with that and use pretty much anything.
If you only have +12 V, an LM358 could work as long as you only drive high impedance inputs, but in that case you might want to shift the input signal a bit to keep the output away from the minus rail (the LM358 is minus rail in, near minus rail out).