I recently replace my through the wall AC in my condo and the cord will not reach the outlet by approximately six inches. The air conditioner modelis an LG 123CNR. The plug is three pronged and hase 2 flat and one round prong. On the plug it details 6-15P and 240VAC. I can't seem to find an extension cord for this type of plug anywhere. I have gone to home depot, sears and searched the web. Would someone please help?

Are you sure you are looking closely enough? I am almost sure I have seen them in the big box stores.

They can be had from 3' to over 10' long.
Here is one: PowerFig PF61514E120 Extension Power Cord NEMA 6-15 Plug to NEMA 6-15 Connector 10 Feet 15a/250v 14/3 SJT - Our Item #: 4498, Category: Power Cords : StayOnline.com

Use the shortest one you can find.

This should be a dedicated line. If you're lucky, the outlet is on the side of the stud toward the short cord end. Use an old work box and try to move the line closer so you don't need an extension cord. Safer that way.