Taking inspiration from this thread and combined with a day off, I present a smartlist script which finds the missing issues in a series and displays the start and end of the gap.

New Version
NEW: Zip file configured for ComicRack's package manager. Thanks cYo!
0.4 Changes: If series is left empty, the script will now go through the entire library and find any missing issues. This requires a well organized library to work really well

If series is specified but the volume is left empty the script will now go through each volume separately.

Installation:
Put FindMissingIssueGaps.py into your scripts folder.

Usage:
Create a new smartlist and name it whatever you want.

Right-click on the smartlist and click edit.

In the configuration window set the first drop-down box to User Scripts and set the second box to "Find missing issue gaps".

The options are:
The first Text Box is the Series Name and is not case-sensitive.
The second Text Box is the Volume number and is optional.


Known Bugs:
For some reason ComicRack runs smartlist scripts twice when you select a smartlist, so any error messages will be displayed twice.
Fixed for version 0.3.1: Crashing when encountering a non-numerical character in Number field, issue is now skipped

If anyone finds any bugs or wants to request a feature, needs help, or even creates their own version, don't hesitate to post a message.

This version outputs the missing issues to a user seletected text file. Find it in the File->Automation menu.

Edit: Somehow I double-posted. Anyone know how to delete a post?

Hi, I have now my hands full with sorting own the problems with my own script, but this is really appreciated... I can't wait to give this a try!

This sounds sweet as hell. Gonna try it out right now.

Nice work, Stone. This is definitely helpful. Especially if you're looking to fill in gaps in a long-running series. If you're like me and use a robust "details" view, scanning down through hundreds of three-digit numbers can be tricky.

New version:

0.4 Changes: If series is left empty, the script will now go through the entire library and find any missing issues. This requires a well organized library to work really well

If the series is specified but the volume is left empty the script will now go through each volume separately.

@doolittle:
I'm glad someone can find some use out of it.

I've added you to the scripts group.
If you want you can add your script to the download section.

This is amazing how well this works. I tried it last night on my collection and was surprised at how well it worked. This has been needed for some time. Thank you for putting it together.

@cYo:

Cool, thanks. I'll get it uploaded when I have time.

@tellsworth1:

You're very welcome. I have been learning python recently so this was a good way to get some practice while creating something I would use.

Sweet! Works great so far!

Thanks a ton!