I want to say that LMC used to sell pre-bent lines, but I'm not sure if anyone still sells them. Pretty sure I saw someone that had them just recently, LMC, Rockauto, Jeffs Bronco Graveyard, or the like.
I've always just made my own. Lots of times, it would be tough to get a full pre-bent piece in place. Easy enough to do at the factory because it can be put in before a lot of the other stuff. I used to buy bulk coated steel line with steel fittings (like $20 got me a handful of fittings and 25' of line), but with the rust around here, they would only last a couple years. Stainless can be tough to work with, but you can buy bulk stainless line and fittings through Summit Racing. After a brief experiment with it, I started making all my lines with Nickel Copper alloy (Ni-Copp). Easy to bend and flare and doesn't rust or corrode. Just turns from gold to green. I use brass or stainless fittings on it, stainless fittings I buy from Summit, brass fittings from wherever I can source them when I need them. I got a double flaring tool from the local auto parts store a long time ago that works just fine. Ni-Copp line is expensive (I just got a 100' roll for around $100 off Ebay), but IMHO, it's worth it.