Wow. Good question. You are making me think about what I did years ago in starting my project.
I purchased a donor alpine in Dallas Texas (about 800 miles from where I lived at the time). The car was a stripped down to just a partial body. From that car I was able harvest a rust free trunk floor and a partial front clip that include the driver side fender and the radiator support.
I purchased front frame rail extensions from a gentleman in Illinois who had parted out a car.
I purchased a new front valance top from Doug Jennings in Dayton, Ohio. I think he said that Rob Martel had made that piece. I do not remember where I got my front valance but it was dented and needed a new valance top.
I hand fabricated the front and rear, rear wheel opening corners by hand using a metal brake, English wheel and shot bag/hammer.
I made the driver side floor pans using a bead roller.
I had purchased the exhaust pipe x-frame replacement pieces but don’t remember who had fabricated them.
The rest of the patches and repairs were made from appropriate gauge steel as needed.
The pan hard bar attachment on the frame rail had been totally ripped out, leaving two holes in the side of the frame rail. That took a bit or reinforcing and repair.
The metal at the end of the x-frame/front spring perch area where the traction master perches were welded in was fatigued and cracked and badly rusted. That took extensive repair and reinforcing.
I had not undertaken a metal work project like my Tiger before and I learned as I worked the project. That is probably why I spent six years of weekends and some nights getting it done. I must say to undertake the extent of repairs that my car needed it was imperative to have the car on a rotisserie.
Before I started the project I had the car chemically dipped to remover all the paint, bondo and undercoating AND had the rust chemically dissolved. I believe it was a Redi-Strip process. I started with bare metal and exposed all the ‘sin’ in the body so I knew what had to be done.
I hope that helps. I will attempt to put a picture story together on the front frame rail extension repair to show you what I did. Hopefully I did it right.
I am sure there are sources for what you need. It may take a bit of networking and parts chasing but you can get there. I would start by posting your needs in the ‘wanted’ forum here. You can check with junk yards (auto parts recyclers) on the net. Good luck.
Updated with photo story: