Probably french threaded, which is more difficult. Can start by taking the spindle (both pieces) to your local bike shop of choice. Some keep a box of random parts, you can get lucky. If you don't have the tools, you will need the bike shop to disassemble it for you. Keep all the parts! Those french threaded cups are hard to find too.

But before you do anything, take some pictures of what failed, so we can target the right part for you.

Visit the park tool site, they have excellent repair details. Even if you don't plan to do the work yourself, it is better if you understand what the shop needs to do.

Those spindles are pretty robust, so I am having trouble understanding how it broke/where it broke. And the spindle is shielded from any direct impact from a crash, whereas the crankset is directly exposed. Spindles commonly are carbon steel, and stronger than the alloy crank attached to it. Are you sure you didn't break a crank arm?? Take some pictures.

If it is a crank arm, you might be best served by picking up a vintage crankset and replacing the crank. They sell on ebay all the time. See the park tool site for details on how to do this job (its pretty simple, but takes a special tool).

It would be great if you took scans of the catalog for the bike and post.