How do I get a fucking Sludge Wave Gengar? I wanted to do doubles with him and Steelix with Earthquake but despite Sludge Wave being a TM, Gengar's line can't learn it.

Alternatively, suggestions for an Earthquake-immune replacement for Gengar would be appreciated, but I can't think of anything that isn't a FoN guy. I just feel quite upset about this overall that I missed out on this