Currently no one is reproducing the front frame rails, you'll have to find a used set from a donor car. You can use any rails from 67-76, but it looks like your '74 might have a shock mounted front bumper? If that's the case you'll need '74 and up for the rails , or you'll have to add the shock mount bracket location to an earlier rail. Or lose the shock mounted bumper in favor of an earlier one.
Are the rails just rusted out where the suspension mounts? It's pretty common for them to rust there and you might be able to just do a patch/section if the rest of the rail is decent. But it depends on the rails of course.