Where do I find <this kind of file> posted to Usenet? - Is a complicated question because of the myriad types of files, and the many "grey" areas between specializations, and the general "sloppiness" by posters in keeping particular types of files in the groups dedicated to them, but there are some established practices to help guide us.

We need to establish categories to clarify the matter. To keep things consistent, we can begin with some categories used in dupe-checking releases, such as: Utils (with sub categories ISO and non-ISO), Games (with the same sub-categories, plus, to the ISO category we add further sub-categories for PC, Console, MAC), and so on; MP3's; Movies (with sub categories for DivX, VCD, SVCD, etc.)

We're going to give you a running start, but you will have to examine your server's full groups list to see what is available to you.

Look for common factors in the names of the groups within any given category or sub-category, and if you see such factors in a group name that is on your server, but which is not on this list, by all means get headers there and examine the content. This list is only a starting-point, and is not meant to be complete, were it to try, there would be 100,000+ groups, with many listed in multiple categories, hardly a reasonable proposition to categorize here. Remember that newsgroups are frequently added or removed from servers for different reasons, so you may or may not have a group listed here. This table is only a jumping-off point with enough information to get you off on the right foot.

One further note: Warez is sometimes posted to groups that don't "sound" like they have anything at all to do with warez. This is the preference of a particular poster, or because some posters wanted to be less noticeable, or "just because."  If you don't get a "heads-up" for such a group they can still be found: Try re-getting the groups-list from your news server in something like Outlook Express, which will show you the number of posts reported to be in each group, then scan the list looking for groups that seem to have an unusually-high number of posts. For example if you scan the list and see a group with a name like alt.binaries.boneless, and that group has 5,000 posts in it, it is likely that some sort of interesting activity is going on there. Get headers and take a peek. 

Main Category:

Sub-categories:

Groups:

Utils:

Games:

alt.binaries.games.psx, alt.binaries.games.xbox

alt.binaries.warez.games, alt.binaries.warez.games.0-day, alt.binaries.boneless, alt.binaries.games.worms

Movies:

Operating Systems: