Phew! Just in case anyone else is in this situation, the folks at https://derailleurhanger.com/ were very helpful and helped me find one that fits: it was the "Hanger 49": https://derailleurhanger.com/product...eur-hanger-49/ which is a little smaller than the one in the photos I posted.

However, this is stretching out longer and longer - it seems that in the accident I had the front derailleur also broke, and it is hard to find one that fits this Eclipse bike.

Does anyone have any advice on how to find a front derailleur hanger that works?

The mechanic said they tried a Shimano Sora Braze-On front derailer hanger but it is a very tight fit and maybe an older model (10+ years older) would work, but they cannot find the part.

Thanks so much! It would suck to have to buy a new bike after all this effort, because it is only a few dozen dollars for these parts, although they are proving to be very hard to find for these Eclipse bikes.