A 400 volt, 100mA SCR (to-92 case) should work, if an SCR is the right device to use. How much voltage comes out of the piezo trigger? If it is the type used to ignite propane stoves, it will blow up the SCR.
Look for C106B , it's a older part, but still made by many. I think it was originally made by GE or maybe Motorola. It's a garden variety SCR, 4 amp, 200 V part, in the "B" designation. Used in light dimmers, etc. There are lots of package and lead variations, identified by numers after the "B", so check the datasheet of whoevers version you get.
Here is another circuit, with remote operation via optoisolator. May be more suitable to your planned use. It comes with an explanation of how it works, and how to build etc.
A 400 volt, 100mA SCR (to-92 case) should work, if an SCR is the right device to use. How much voltage comes out of the piezo trigger? If it is the type used to ignite propane stoves, it will blow up the SCR.