The part number of the standard crankshaft is 260271. There are something like a dozen others used on 60102 engines, and all of them may be usable on yours. Here is the Illustrated Parts List for your engine:
http://bsintek.basco.com/BriggsDocumentDisplay/18lowGXBnfBhU7y.pdf

However a new crankshaft will cost at least $120 plus shipping from the US. A deal like this might be more attractive:
http://www.ebay.com/itm/VINTAGE-BRI...-ROD-PISTON-kart-minibike-/161215829542?

The 6 cubic inch horizontal-crankshaft Briggs engines are very popular for minibikes etc in the US. That means there is demand for the parts, which is not a bad thing because it means people will list them for sale.