Never seen an alloy sealing washer in that location Ted, always been copper and I’ve seen hundreds over my time, as are the ones under the socket bolt under the fork slider. Part number is 90453-273-000, look at any picture of that part number and you’ll see they are copper.
Brake line ones are usually copper as well although alloy for both of the above could be used, it’s just a crush washer when all’s said and done, so long as it seals that’s all that’s important.
Btw the genuine washer for the drain bolt is around £1 odd each, just buy a normal 6mm copper washer off eBay and save yourself some money, same goes for the socket bolt washer, says special packing washer in the Honda description but there is nothing special about it really, same for sump bolt sealing washers, buy them off eBay, cheap as chips.