Here is the Illustrated Parts List for your engine, in case you want to have direct access to it:
http://bsintek.basco.com/BriggsDocumentDisplay/18mrxLXCnfBhU7y.pdf
By referring to that IPL I found the same part numbers for the required items as you did.

The Outdoorking on-line store lists one of the three parts (499901), or you can get it on ebay:
http://www.ebay.com.au/itm/Briggs-S...mowerAccessories&hash=item43c2287582

The other three parts are not listed at the online store. You could contact the store and ask them to get them for you, or you could get a kit containing all of the remaining parts (2x281505S pawls, 1x691855 circlip, and 1x692299 pawl friction plate) on ebay:
http://www.ebay.com.au/itm/Briggs-S..._DefaultDomain_0&hash=item1e7cb2dc30