o.k..so, if you find a stock rooted rom for your specific device, you can download the rom.
Once downloaded to your computer, you can unzip the rom file (as it will download zipped up).
Find the apk and the path to your app you deleted, perhaps /system/priv-app/keyguard.apk.
Copy that apk (from the unzipped rom) to your device. Put it somewhere you can find it with ES File Explorer.
Now, I personally use Root Explorer but ES File explorer should perform the same function.
Open your file browser (ES File Explorer) and navigate to the apk file. Copy the file and move it to the path it came from.
Paste it, set the permissions to match the other, existing apk's and reboot..
It's been quite a while since I've done this so if I'm missing anything, I hope someone will correct me
By the way, did you make a nandroid backup of you current rom? If so, you could probably extract it from that.
What is the Model number of your device? I can try to help you find the apk.