https://www.zotero.org/styles/

for requesting new style follow instruction on https://github.com/citation-style-language/styles/wiki/Requesting-Styles

Thank you both LiborA and adamsmith, I will follow the link!

Ok, so these following are the information required for creating the new Style OECD:

https://www.oecd.org/site/eduimhe08/guidelinesforauthors.htm

https://www.iea.org/publications/freepublications/publication/IEAOECD_style_guide.pdf
pages from 19 to 24

ie.

In-text citation:
(Campbell & Pedersen, 2007)
(Mares, 2001)

For more than three authors, the in-text
reference should cite the first author followed
by “et al.”.

Bibliography:
Campbell, J.L. and O.K. Pedersen (2007), "The varieties of capitalism and hybrid success", Comparative Political Studies [name of the journal is in italic], Vol. 40 (3), pp. 307–332,
https://doi.org/10.1177/0010414006286542

Mares, I. (2001), "Firms and the welfare state: When, why, and how does social policy matter to employers?", in Varieties of capitalism. The institutional foundations of comparative advantage [italic], P.A. Hall and D. Soskice (Eds.), pp. 184–213. New York: Oxford University Press.

Could you please create a style like that?
In the links at the beginning of the post you can find some examples.
Thank you very much in advance.
Please let me know if I can help you further.

@TattoStyla
Have a look at this. It'll likely have some mistakes, since I just put this together quickly. Let me know what needs fixing.
https://raw.githubusercontent.com/POBrien333/styles/826bed7c987f7537136f10892f4bb0e3fdb6e8b1/international-energy-agency-organisation-for-economic-co-operation-and-development.csl (right click and save as)

@TattoStyla
Style now available on the repository: https://www.zotero.org/styles?q=id:international-energy-agency-organisation-for-economic-co-operation-and-development

I am currently preparing a document using the OECD style guidelines and it appears there have been some updates to the style since this thread was originally posted.

In-text citation (brackets and citation numbers are subscripted).
(John L. Campbell, 2007[1])
(Mares, 2001[2])

Bibliography
John L. Campbell, O. (2007), “The varieties of capitalism and hybrid success”, Comparative Political Studies, Vol. 40/3, pp. 307-332, http://dx.doi.org/10.1177/0010414006286542 (accessed on 26 July 2010).
[1]
Mares, I. (2001), Firms and the welfare state: When, why, and how does social policy matter to employers?, Oxford University Press.
[2]

In the examples above the author and publication info appear on the left, and bracketed numbers appear in a column to the right.

Here is an example of the citation style in a publication freely available on the OECD website. The bibliography starts on p. 180:
http://www.oecd.org/chemicalsafety/risk-management/measuring-the-effectiveness-of-best-available-techniques-policies.pdf

OECD does provide an MS Word template for authors that includes a .xsl style for the Word citation manager as well. Is there a way to covert that to a. csl style and import it directly into Zotero? It is available here: https://community.oecd.org/docs/DOC-151536

Thanks adamsmith. I see what you mean--I just checked out the OECD Style Guide, 3rd Edition and it doesn't appear to reference this style. I did find some additional guidelines for external contributors here https://community.oecd.org/docs/DOC-129302

There is a note that says "There are some differences vs the OECD Style Guide (3rd edition). For example, it is no longer necessary to add a letter to distinguish sources by the same author published in the same year. The Style Guide will be updated accordingly."

So, it is possible this style will be reflected in the updated style guide. In any case, the guidelines do indicate that OECD wants external contributors to use their Word template and they don't want authors using third-party add-ins, so it appears that I am out of luck with this one.

I was able to find a workaround that allowed be to avoid entering my entire Zotero collection manually into the Word citation manager, however, based on this older post of yours https://forums.zotero.org/discussion/comment/206394#Comment_206394

I exported my Zotero collection as a BibTeX file and then used bibutils bib2xml followed by xml2wordbib. This allowed me to convert the library into a format that could be imported into MS Word.