They dealer is correct. The 2 metal spring clips are deemed part of the headlamp and aren't listed as separately available parts. I think you're going to struggle to get one without purchasing a complete headlamp unit unless someone has a damaged headlamp and are prepared to sell you just the clips, but it would be like finding a needle in a haystack.
Which clip have you lost, top top or bottom one?
You're probably going to have to come up with a bodgy solution to prevent moisture getting into the lamp until you can find a more permanent resolution.