During my resto on my custom '68 I looked all over hell and high water for one, could not find one that was worth looking at. Even Lectric Limited will not sell just the box. I would ask yourself the question though, if you need a new fuse box, it's probably due to corrosion, and the corrosion probably occurred over the past 49 years. If so, your existing wiring harness is probably just like mine, the insulation is hard, brittle and cracked, and under the insulation, lots of unseen corrosion in the wires. I know a new wiring harness is about 4-5 hundred bucks, but mine was worth it. The last thing I wanted to do was get my interior all finished and later need to replace the harness.
I replaced all the harnesses in both my '65 and my '68. The harness in my '65 was just old, but the one in the '68 was a disaster. No wonder I had all the electrical problems I had with the car. Now, none.
Your choice, just my 10 cents!
"There never seems to be enough time and money to do it right, but there is always enough time and money to do it over!"