Adding to my first response, please note that you can certainly approach colleagues to critically read your manuscript(s) for comments and advise. You can ask for such help from your peers without offering coauthorship. Acknowledging such support at the end of the paper is a nice and reasonable gesture.

The title of your question makes me cringe - coauthors are not a commodity you can simply pick and choose to add to your papers, and there are clear ethical rules what involvement merits a coauthorship. Simply asking somebody to be a coauthor on a near-finished paper is unethical for both persons involved.

Coauthorship starts with a collaboration, which in time may lead to the cowriting of a paper! If you go to an international conference every year, this should have given you an opportunity to start collaborations or at least helped you create networks - that's what conferences are all about ;-)

In your situation, don't forget to weigh in the merits of publishing single-author papers. Although I usually don't consider this a major merit in natural sciences, many of my peers do.

My reply is too long to fit into this little RG box, so I will send you RGmail. {Scrolling? What's that?}

If you can publish your work alone (if your papers are good enough), you do not necessarily have to find co-authors for your papers. A real co-author would also want to change something in your work, not just add a name (although you can probably find several people like that, too). It would make sense to find somebody who could e.g. add data from another country or who could rewrite the theory part using a different angle. If you wish to find such people, go to conferences, visit their lectures... sometimes it is also fine to send e-mails to some people who have similar interests (e.g. whose works do you usually cite: maybe somebody of these authors can become your co-author).

Adding to my first response, please note that you can certainly approach colleagues to critically read your manuscript(s) for comments and advise. You can ask for such help from your peers without offering coauthorship. Acknowledging such support at the end of the paper is a nice and reasonable gesture.

@Janos, You have got good answers. I do understand Your position and I was very familiar with! So, You do not have to apologize for question asked! In many countries that was common practice! So, follow the instructions from previous comments and fight for your place in science community with respect to the moral standards and ethics! Regards!

Interesting question. Authorship is considered by many as a currency, but not in the way your are pointing, but is not uncommon that the head of a department (or similar) ask for authorship in order to not interfere with your budget, your ideas, your work, etc. In this case you are not talking about this, you are talking about “enrolling” coauthors. It is quite peculiar that if you are starting to build your reputations you ask for coauthors that MUST collaborate with you in your field of interest. My advices is find someone who is close enough to your interest, with a very well established reputation and if it is possible, look for a grant to stay for some time as a postdoc with that person. That will give you the chance to expand your interests, and certainly will give you name and reputation within your field. Then you can lead whatever topic you want, no matter how un-sexy your ideas are.

Thank you for your comments.

@Ernesto: In my country, postdoc grants are almost out of reach for the majority of soft scientists, for various reasons but mainly 1.) universities very rarely offer postdoc grants and positions in those areas 2.) most of us can not compete scientometrically with hard scientists or colleagues who work closer to hard science fields, like mathematical statisticians or computer logicians (and oc committees evaluate all applicants by the same standards). Nevertheless it is a good suggestion, i will give it a try next year.