Hi QSR,
The only place I've seen them for sale is eBay, the minimum price was $250. for two replica side skirts ,the bolts
also have been reproduced
On eBay user name oldmachinerybloke makes some parts for Victa 18 mowers on a Lathe ,you could
ask him to machine up some victa 18 side skirt bolts.
Otherwise it's just waiting until they are advertised online.
Original side skirts could be 4 times the replica price or more as they are rare.
Cheers
Max.