Are there consumer ALUs in the GHz range?
It simply can't be done at that speed as a standalone chip. The ALUs in an Intel or ARM CPU chip only have to drive a limited amount of nearby circuitry on the same chip, which is why they can run so fast. There's no practical way to get the drivers required to send those signals off-chip to go that fast.

Even general-purpose CPUs only ran at tens of MHz initially. It was only the development of on-chip caches, which decoupled the CPU speed from the external bus speed, that allowed CPU clock speeds to break the 50 MHz barrier.