I am also searching for this file. I have tried no less than 3 times to buy a support contract for this switch from 3com and they have NEVER completed the transaction... what a stupid setup they have.
Anyway, I'd really love to update my firmware as well... I'm sure there's some system stability to be gained as the web console is continually flaking out and requiring a hard-boot of the switch to regain access.
So, if you have any luck finding the elusive s3m06_10.exe -- please pass it along.
I was having the same problem with the support contracts. Nevertheless, I was able to obtain the file from another source. Email me through these boards and I'll give it to you.
I also need this file! If someone finds a download link for this that works, please post it here! The file isn't even on the CD that came with brand new switches so stacking new and old switches together is likely to be unreliable!