As of Scarlet/Violet, the latest and simplest way to get egg moves on any male Pokémon is through using Mirror Herb in a picnic. Directly quoting Bulbapedia,
In Pokémon Scarlet and Violet, if the player has a picnic with one Pokémon that holds a Mirror Herb and has an empty move slot, and another Pokémon that knows a move the first Pokémon can learn as an Egg Move, after the picnic the first Pokémon will learn that Egg Move, even if there is no matching Egg Group or if both Pokémon are of the same gender. This does not consume the Mirror Herb.
This allowed for the Male-only Pokémon who once never had egg moves to finally have them! Despite this however, even in previous generations, a myriad of Male-only Pokémon were able to learn egg moves through a few similar methods:
Through Breeding with a female-counterpart of their Evolution Line.

This only really applies to Gallade, as Burmy is incapable of learning any egg moves, but by breeding a female Ralts/Kirlia/Gardevoir with any male Pokémon with an egg move, you can simply hatch a male Ralts and evolve it into a Gallade no problem.
Through Breeding with a female-counterpart of their species


For both the Nidoran♂ line and Volbeat, the female-counterpart of their species, being Nidoran♀ (as Nidorina/Nidoqueen cannot breed) and Illumise, both have an equal chance of producing an egg of either species, allowing for Illumise to produce Volbeat eggs and Nidoran♀ to produce Nidoran♂ eggs.
Through Breeding with their Evolution Line's alternate Evolutions

Exclusive to Tyrogue and Hitmonchan/lee/top, when breeding with a Ditto, either of the Hitmon's can produce eggs of Tyrogue. As a result, these eggs can evolve into any other Hitmon, allowing for, say, a Hitmonchan to pass eggs move onto a Tyrogue, which then evolves into a Hitmonlee.
Additionally, methods of obtaining egg moves beyond breeding, such as the BDSP Grand Underground, work just the same for male-only Pokémon.