Where can I download the latest version of the Yu-Gi-Oh pc game (if available)?
According to the Wiki, Yu-Gi-Oh! Power of Chaos consisted on a series of three games, which were (in order of release):


Yugi the Destiny
Kaiba the Revenge
Joey the Passion


Seems that there are no further releases of the Power of Chaos series.

As for where to download or buy there are several options, so the best would be to Google the specific release of POC you seek and chose among the options (I also want to refrain from promoting a specific page or product)

A quick search revealed several sites that offer download, and I am sure that you could find it on places like Amazon or EBay