I think I would buy them from Calvert unless a huge discount was found somewhere else.

You can get their recommendation for what spring you need.

A long time ago I purchased bars and springs from them, turns out it had too much rise leaving the line.

I sent them photos and they sent me a new set of springs and while I returned the first set they never asked for them.

Their customer service would probably still be great if you bought the stuff somewhere else but I would still rather deal with them directly.