CAN I TAKE AN OLD RIM REMOVE THE GEAR CLUSTER AND REPLACE WITH ONE GEAR USING SPACERS AND DO YOU KNOW WHERE GEAR AND SPACERS CAN BE HAD?
Go to a bike shop.
you can, depending on the hub type, but the rear tire won't be centered.. you would need to get the rim trued by someone who has the right tool (Park truing stand usually) and knows how to do it..
Actually, the rear wheel will be centered, just with the same dish that it had as a multi-speed wheel. You just have to arrange the cog and spacers to make a good chainline with the chainring.
Conversion kits containing spacers and a singlenator are available from bike shops.