Basically for these fungi, only different "sexes" can reproduce with each other. Still only need two for reproduction. They can't reproduce with the same sex. So A can mate with B, C, D, etc. A can't mate with A. Do dna sequencing on a few that you know can mate with one another and you can find where the sex allele/gene is. Then you can sequence the population at large to see how many different sex alleles there are. You can confirm or do old school observation to see which ones can reproduce with another.