I'm curious about this as i do strength training myself and looked into it before i decide to head back over.

Yellowhat, as far as im aware there is a Gold's gym in Tokyo (i think in the Harajuku area). So pretty much that will have what you need but from what i heard it might be quite expensive (although im not 100% sure on the membership prices). There is also another Gold's gym somewhere else in Japan, i think Osaka but thats it.

There are also privately owned gyms around the country that will have weightlifting equipment but obviously might be a bit more harder to find depending.

Hope that is helpful to you