The Kluwer LaTeX style file can be obtained from the publisher:
Kluwer Academic Publishers
P.O. Box 17
3300 AA Dordrecht
A guide to the Kluwer LaTeX style file is also available both in hard copy and in electronic form.
Using either the standard article.sty from LaTeX distribution or the publisher's style file is encouraged but not obligatory. If you use any non-standard style file, you should enclose it with the electronic version of the paper.
V. M. Nesterov