I find those every so often at the salvage yard. I'm going there next week. They usually charge me $10 for an elbow...or for any duct for that matter. I usually just pass along the price to members of the forum....just because I'm a nice guy and want to further the hobby. I do have one elbow on the shelf...but unfortunately it's not perfect. It has a crack where it joins to the lower duct. And, the crack is on the top so it would be noticeable. If I find any elbows, I'll PM you two.
They are kind of a hard part to find because they either get taken off or break. Are they worth $150? I guess so because I've seen them go for that price more than once.
I'll also check the box they have in the storeroom. I know they had two or three of them there the last time I checked. I think one was for a 75 though.