Question: The male klepton is a unique humanoid. It has no females, and reproduces by mating with other humanoid females, who bear children that are clones of the klepton father. No females are born, and all offspring belong to the klepton species. While a settlement of these beings could simply obtain the necessary mates through kidnapping, this isn't exactly sustainable; raiding cities to enslave their women (or anyone else) isn't exactly good for diplomacy

How could this humanoid maintain a settlement, where most of the population is of the klepton species and the children end up with their fathers, without the need for any kidnapping or sex-slavery?

Answer: 
**Buy brides**, using classic arranged marriages with the brides' families.

[Bride Price](https://en.wikipedia.org/wiki/Bride_price) is the practice of the bride's family receiving payment ([dowry](https://en.wikipedia.org/wiki/Dowry) is the practice of the groom's family receiving payment).

Bride Price tends to occur when 1) Marriageable women are relatively scarce and 2) Manual labor is valued more than accumulating capital. In turn, these suggest the settlement region is fairly rustic, has no banks, and that any local aristocracy are not rapacious.

The kleptons in this region must have a somewhat higher income than their human neighbors, balanced out by the ongoing wealth transfers for each marriage.

It certainly wouldn't hurt if the kleptons tended to be kind, devoted, intelligent, attractive, and clean-smelling spouses, and fairly trustworthy in-laws, keeping the price lower.

The settlement cannot be large enough to distort the region's marriage market -- lots of unmarried human males wandering around have never been great for stability. Alternately, perhaps the kleptons --with their extra income-- can import some brides from distant regions or towns.
**Reproductive technology and commerce**

Have the species forge trade agreements with land based settlements. Then formalize a 'marketplace' where excellent prices are offered to women who are prepared to sell viable, healthy eggs. Establish (or have land dwellers acting as licensed brokers) establish registered clinics where the trade is conducted under the supervision of local (land based) authorities who also get a % via the same tax rate they charge other trades. Then just use artificial insemination and artificial wombs to grow new colony members.