Define the Manuals You Need
The first thing to do is to know which kind of manuals you actually require. Previously these were mainly limited to aircraft and military production but now have a wide array of uses. Know which field are you targeting and which specific ones you need in the given field. This will get you on the right track from the start and will help you save even more time.
Once you are aware of what you are looking for, go to the online forum boards of a related field and inquire where these may be available online. There are always enthusiasts and experts available online who can guide you in this matter and they should be able to point the finger in the right direction.
You can also go to the website of the manufacturer that produce those products and see if they have these available. They may not be free but you can certainly make use of them by purchasing them.
Going to the library can be helpful as well. The library staff is well versed in researching online and they can guide you properly. They may well be aware of what you are looking for as many people ask all kinds of queries all day and they are busy locating topics, both in the library and online. It is quite possible that they will have some of these ETMS or IETMS available with them. They will not be having the complete range on all subjects but will certainly be carrying some of the common ones that are being used by people.
Just about everything is available online these days and do not be surprised if you find these selling on popular online auction sites. You can search for the specific manual you are looking for and check on these websites. Although you are likely going to get a used one, it is better than not having one at all. As long as the CD’s work, it’s not a big deal.