I scoured the web for them, too, but they're not there. For me, at least, they were already in the Redistributables list included with InstallShield 2009. You should also have them if you have Visual Studio 2008 SP1 installed - look in C:\Program Files\Common Files\Merge Modules.
Hope this helps. ...and good luck with them. Tons of problems.
I posted this for another thread, and added here as it may be useful...
When you install VS2008 SP0, the merge modules go into the common files folder, normally "C:\Program Files\Common Files\Merge Modules".
When you install SP1, the merge modules will also go into this folder - but the SP1 installer is poo, and will not update the folder if you have VS merge modules already there.
What I normally do is install VS2008 SP0, rename the "Merge Modules" folder to "Merge Modules.VS2008". Then install VS2008 SP1, you will get a new "Merge Modules" folder. After the install I rename this to "Merge Modules.VS2008SP1". I then create a new "Merge Modules" folder, copying all the "Merge Modules.*" items into it.
The same applies for the other version of Visual Studio. We also keep a copy of the merge modules on our network for backup.
