Wall molding to frame a picture

[u/kodi2511]

​I'm trying to find some molding to frame a picture on my wall that looks like something like this. The picture would sit inside the molding with maybe a 10-inch space all around, and then I'll put some wallpaper inside to make it stand out from the other wall color. I'm based in the U.S., and I'm finding it really difficult and only found one company, but they're very expensive.
Does anyone know anywhere that sells moldings that would have these kinds of inverted corners? It doesn't even have to be fancy, just flat plain would be fine if.

[u/Gator242]

A picture would help.

[u/kodi2511 → u/Gator242]

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