All those kewl Western belt plates are great, but you know what was more common?  Plain roller buckle belts.  If you want a neat one, however, check out this copy of a Macon contractor-marked waist belt.
 
To get the right fit, you need to measure your waist where you wear your belt, in inches.  If you provide your pants size, you're going to get a belt that is far too small.  Take a string, wrap it around yourself, and measure the string.  Or measure a Civil War belt you already wear from the prong on the buckle to the adjustment hole that you use.  The center hole on these belts will be placed at the measurement you provide, so if it doesn't fit that's on you.