Yup, DIAC works nicely for one-shot trigger. For continuous trigger (e.g., where you don't know the phasing of load current, you just want it on at some point), the usual method is a gated clock into a transformer. Since the gate needs at most a couple of volts, a driver from 12V can get plenty of leverage against it with a modest turns ratio. Maybe a few 10s of mA, through a BJT/MOS switch, into a 4-6:1 turns ratio. A series resistor between secondary and gate, and a catch diode anti-parallel with G-K, and you're good.
Of course, if you need more precise timing (within ~µs), it might be that the enable comes along during a low period of the clock and doesn't fire until the next pulse. In that case, either an oscillator-enable can be used (starts pulsing immediately; first pulse may be unevenly timed, like when using a 555 this way), or drive it full-wave into a push-pull transformer, with rectified secondary into the SCR gate (make sure to have a nice beefy pull-down resistor G to K to ensure it discharges when undriven).
Tim