If you only want to find (physicaly locate) the sources where the EMI is generated, you can better invest in near field probes witgh a descent spectrum analyzer. You can think of magnetic loops, E-field probes, current probes, Bowtie antenna (for the UHF part of spectrum), etc. You can find the source with the small probes.
As locating a source of EMI doesn't require accurate equipment, you can make many probes yourself. Search for EMC probes DIY (DIY = Do It Yourself) and you will find relevant info. For locating the source you don't need a real EMC measurement receiver, a descent spectrum analyser is good enough. Be careful when buying ver low-end equipment as the dynamic range and spurious response may not be sufficient. This may result in finding things that aren't there, but are generated by the equipment itself.
If you want to find the frequency range where you exceed the limit, then you need at least a pre-compliance setup and you need to know the standard that is relevant for you. The standard specifies frequency range, measuring distance and height, soil conditions (soil or conducting plate/mesh), polarization, properties of detectors, etc.
So I think that you should start with studying the relevant standards. Then you are better informed to select equipment that does the job for a reasonable price.
To get an idea of antenna equipment you may visit:
https://www.ets-lindgren.com
https://www.com-power.com/antennas.html
These are just examples, there are many more companies supplying (calibrated) antennas.
As the "sensitivity" (E/Vout) varies with frequency, modern spectrum analyzers or measuring receivers enable you to enter the antenna parameters into the equipment so that you don't have to do the math manually.