AFAIK, it's recommended to use a minie that's .002 under bore size. That requires accurately measuring the bore and then sizing the bullets if necessary.

Hornady .58 saboted conicals are listed on Gunbroker and are also available from Natchez:

http://www.gunbroker.com/Auction/Vie...Item=225520016

http://www.natchezss.com/product.cfm...&prodID=HO6726

MMP also sells bulk .58 sabots for use with .45 bullets:

http://www.mmpsabots.com/