Wheel Room Parts Room Cellar Mtn. Frames Road Frames Mtn. Not because it is a mess, although at times it can be caotic, but because it is sunken down below the rest of the store and usually hides some very cool projects.
Any bike can quickly, and inexpensively be made into a single speed.
You have most of the parts you need and the others are not hard to find. The basic ideal is to replace you rear cassette with a single cog and remove all but one of your chainrings. Gearing is different for everyone. If you live in an area that is hilly you may want a lower gear. If you like to stand and mash than maybe use a larger chainring.