RQG p.298 claims that Lhankor Mhy cultists may only marry inside the cult.
I recall quite clearly that earlier cult descriptions had the requirement that Lhankor Mhy cultists were only allowed to marry light cultists, emulating LM's partnership with the Lady of the Light of Inspiration (who may have been Ourania, Mistress of Heaven). It was quite hard to find female light cultists among the Orlanthi, unless you allowed Mahome as lowfire.
My LM character went for an initiate of the Redaylda subcult of Elmal, which went well with the character's fascination with fast horses and attempts to breed ones near Karse from exotic stock. A weird passion for someone from Pelaskite origins and strong in his roots, but anyway...
Then there is Broosta, Daughter of Pavis (the only female one) and Lhankor Mhy initiate, married to Fleeter Nemm, also a Daughter of Pavis. Does her priesthood in the Pavis cult override her LM marriage restrictions?
On the other hand, Broosta gives a model how to get your prospective partner accepted by the cult if only marriages inside the cult are sanctioned. The prospective partner has to become literate and a LM initiate on the side, wearing that weird veil, etc.
(I wonder whether henna tattoos or permanent ones on the chin, possibly in elaborate patterns, may serve for the "fake beard" requirement...)