G'Day Templar I found one for sale so if you have an eBay link just put this number in search and the Battle of Thermopylae coin should come up,
the number is 290325446307 the seller is chrkub05 from Laguna Woods CA U.S.A.though I not sure if you like the price as it's a by it now sale,
the next coin that is the fourth coin in the famous battle set is the battle of Gettisburg and the fifth coin depicts a major battle in WWI or the first world war.
regards Harry