>>43254871200mm prime lens
Kidding aside (mainly due to price), could mount your camera to a telescope and get similar magnification levels at a more realistic price
Other solutions... digital zoom? I mean if you were shooting on a gfx100 or something, could always crop in to get a bit closer as well
If you shot on MFT you'd already have twice the equivalent focal length due to the sensor size as compared to a full frame camera so that might help a bit.