Hello, zander811! Welcome to Lucasforums!
One thing that you can take a look at is baseitems.2da. This is in the BIFs section under 2da.bif. What you can do is find the pistol row (row 12 for KotOR 1), and copy it (right click on the gray box to the left of it). Go down past the last line where there is a blank line and type is anything in the first column. Now right click the gray box next to this line and hit paste. First change the Row_Label to the next number in sequence, and set the name to -1 or ****. Change the label to Saber_pistol, or whatever you would like. Change item class to w_lghtpstl. Now scroll over to the default model and change it to w_lghtsbr_001 (for K1 at least, not sure about TSL). Save this in your override folder.
Under the Tools tab at the top of KotOR Tool, open up Options. Make sure that under Other, 'Look in Game's Override folder for 2DA files' is checked. You should probably restart the KotOR Tool.
Now, you're going to creat an item for this. Under BIF's, go to templates.bif, and expand Blueprint, Item. Find g_w_blstrpstl001.uti. Double click on this to open up the item editor. Now, change the Template ResRef to g_w_lghtpstl001. Change this tag to this as well. Under Base Item, scroll down until you reach 'Saber Pistol.' Choose this. You can change the Description tab to whatever you like. save as g_w_lghtpstl001.uti in your override folder, and be sure to include the .uti extenstion.
Start your game, and type in giveitem g_w_lghtpstl001, and you should have a lightsaber pistol dual wield. It won't have a custom icon, but I can go over that it you'd like.