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: 
**Animal mother.**

As you set it up, the klepton DNA evicts DNA belonging to the egg of the mother. Or more likely the klepton "males" actually are neither male nor female, but mitotically produce a single cell clone of themselves that has the ability to parasitize the reproductive tract of a female. A gamete like a sperm is a product of meiosis and cannot give rise to a clone of the parent because meiosis shuffles the genes. The kleptons are male only in that they use a penis to place the zygote in the host female.

There is no need for the female to be humanoid or sentient to participate in this endeavor. She does not contribute DNA. She only needs to be the right size to gestate the klepton. A large domestic animal would be fine in this role.
**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.