So, it seems to me that at high levels, waiting around in a city trying to recruit mercenaries for your domain is awfully droll. As there are people you can hire for training your animals, training your men, supplying your men, keeping their weapons sharp, etc, may I suggest adding someone who hires them as well?
A military recruiter specialist would be pretty handy.
You can extrapolate the availability of specialists requiring different numbers of proficiencies using the Hireling Availability chart: A specialist requiring one proficiency shares the availability statistics of Healer. Those that require two proficiencies, the Healer/Physicker line (with a variant in availability and wages for ship captains). At three proficiencies, the Healer/Chirugeon line (with a variant for Sages).
If you look at the proficiencies chapter of the core rules, the Manual of Arms proficiency describes the various levels of proficiency needed to train different types of mercenaries. If you allow Weapon Focus to be reckoned as a proficiency available to some NPCs, those patterns will let you determine the availability of trainers for all the human mercenary types except for cataphract cavalry, which requires a trainer with 4 proficiencies. I’d personally use the Sage numbers there.
If you don’t want to deal with Weapon Focus that way, then you need to work out a way that you’ll combine the availability of specialists with the availability of first-level Fighter NPCs.
Sorry, seeing that I might have misread your post (though I don’t think my answer is irrelevant, regardless). I think the costs of recruiting indicated in the DoW indicate that your character is not personally doing all the recruiting- the example text indicates that a retainer may act as their representative, and the scaling cost with land suggests that there are additional staff being deployed. As a Judge, I would probably require a player to at least have their recruiting affairs managed by a retainer, but if you don’t feel the need to do that you can always tack on a cost for a trustworthy 0th level administrator to the recruiting costs.