I would start by trying Home Depot or Lowes. If you can't get an exact match, I'm sure you can engineer one to fit and it'll prolly be of better quality. BTW, why are you replacing the rollers, did one break?
2010 Cedar Creek 5th Wheel 34SATS "The Beast"
2006 Ford F350 Lariat 6.0L Diesel
2003 Harley Heritage Softail "Hogzilla"
1988 Harley Softail Custom "The Fireman"
1986 Marriage to "Wifey" (patience of a saint)