Just bite the bullet and pay the £45 or thereabouts from the dealer. You can find them secondhand, but they are normally the wrong size or in poor condition. No-one has found a decent aftermarket copy as far as I know.
I just bought a pair of anniversary badges from eBay, the front is 74mm and I think it looks really good! I had to use some 3m VHB tape to hold it in place... The rear was a straight replacement...
