I can operate in wavelengths ranging from 2200m to more than 13cm, generally but have access to sumbillimeter regions of the spectrum as well which is well past what is considered microwaves.(1) The amateur radio has a band; AM radio has 10KHz. So amateur radio you use must have a band, that is an area in the spectrum rather than a line as maser is. Even tunable laser (maser) can have several frequencies, but just one frequency can appear at any moment.
SO if this equipment is available at the consumer level then it's probably not illegal. Also, the uses that you, that you consider it the users right to bombard you, seem to fly in the face of what you consider harassment.(2) 20 years ago, the infra-sound might be illegal to own in U. S.; in 1960's, it was a huge speaker (which was really inconvenient to handle). These days it is very common in some country (area), where residences, apartments, are "stacked" into concrete buildings, 10 stores or higher. When the residents above "your" ceiling is too noisy, all "you" can do is using infra-sound hitting your ceiling a couple of times in order to tell the people above "you" "please be quieter". There are many sizes sold in stores or that place's local internet. If some one wants to hit by using the infra-sound, I think that it is totally up to him to decide.
The part of this equation that you continue to refuse to answer is they "why"? Why would your neighbor continue to go to the expense and trouble of bombarding you with masers and infrasound? That would make the neighbor and nutty as you sound. Being able to answer the "why" would also be crucial to getting someone to actually investigate. While you speak of having a frequency analyzer it's also likely consumer grade, due to expense, and would not be sufficient for your purposes.One other issue is the microwaves aren't too good at penetrating solid material. Generally as wavelengths get shorter the ability to penetrate solid matter is diminished.
I'm going to recommend that your build a Faraday cage around your house for the masers and that you invest in a giant set of Bose noise cancelling headphones that would, likewise encase the house.