For the moment I am paying a ridiculous 20k per spike.Also buying charged steel spikes at no price difference.200k for charged inguts./v +hyperbeam on smp8 You get them from enraged silverfish. Enraged spawns must be on in player settings (/ps). They spawn from any kind of natural spawned ore in the over-world at any y below sea level. Use fire potions and melee to avoid low risk detection. I am also convinced you need to be using a non-silk pick. I see no need to test this because I wont risk wasted effort. Not sure it must be below sea level but I can confirm that I have spawned one just below that. There is another method but I have not had much luck doing it myself. They can spawn from monster blocks which are in end portal dungeons.(non-silk definitely required) I'm convinced spawners do not spawn them.
I'm pretty sure you can use a silk pick, I have fought over 10 of them and I only use silk picks, however, there is a chance that maybe they have all spawned from ores which are not effected by silk touch.