The Regex shown in the script does in fact match "3750", however it is likely that the way the Model is being reported via SNMP (and subsequently stored in the NetMRI) is slightly different than "3750". For example several Cisco 3750's in our network are shown as having a Model Number of "catalyst37xxStack" on one my NetMRI.
You can verify this by performing an SNMP Walk (Tools>Device>SNMP Walk) of the system OID for a given device, as well as looking in the Model field in Network Explorer>Inventory>Devices>Devices.
Using this information, you can edit the regex to accomidate, or even "hard code" in a specific Model string for the $model variable in the script filters.
If you experience any further problems on this please follow-up with an email to support@netcordia.com.