I may look at stocking male LMB. How is it possible to source them with high degree of certainty? (Near 100%)

12 yr old pond, 1 ac, 15' deep.
RES, YP, GS, FHM (no longer), HBG (decreasing), SMB, and HSB (only two have been seen in 5 yrs)
I think that's about all I should put in my little pond.
Otter attack in 2023.