I'm not sure how many variations there might be for different levels - 32bit, 64bit, Network and so on.
You probably need to look for a file named something like Monarch ......._Upg.exe
The dots represent the part of the file name that likely identify the version and release.
That said the name may be something completely different. I have been known to rename files when they arrive with a name that is likely to be unrecognisable for future re-use.
Date wise you are likely looking for something from 2010 but that assumes Windows shows you the original file creation date and not something related to when it arrived on your system or was saved at some point.
If you find some candidates the Properties should help to ascertain whether it is the right file. But feel free to ask for any clarification you may need and I will see if I can be of assistance.
I have uploaded the original 10.5 patch file for you.
Please click on one of the following links;
These links will expire in 7 days (9th March 2018)
This is the original 10.5 patch file. In my library, its called 'Monarch Pro v10.5 Upgrade.exe'. I cant guarantee that this is the original patch file name -
Not also that the file is provided with no implied warranty or support given the end of life of the 10.5 product. It was never designed for execution on a modern OS as these supersede its originally intended deployment scenarios.
Hope this helps!