I don't have any seedlings but it has been awhile since you posted and no one seems to have responded. You should attempt planting more seeds preferably seeds grown for this year. The key for germinating seeds like those is warm soil. You could likely plant them outside at this point, but I know some people put pots on top of the refrigerator where it is warm for better germination results. I say just keep trying to germinate seedlings. It would be hard to teach about living off the land if can't tell them how to get the seeds to germinate :) I don't know what your intentions are but if these crops are grown at school with little maintenance I would recommend growing sweet potatoes in the ground as they can tolerate neglect. Or using self watering containers with an automatic watering system. I have seen many gardening projects at schools fail because they were unable to water over the weekend in the summer when the plants are well established and require lots of water if grown in containers.

Unless someone locally has seedlings, it will not be practical to ship them.
Some garden centers sell seeds. Better yet, if there is an Asian market you can buy a whole luffa, cut it open and get some seeds out. This process can also be educational for your students. Once you got the seeds, plant them preferably in ground or peat pots.
Gourds need night lows around 55-60F(min.) to really grow and take off. They may germinate over 40F too but will not move much. Not knowing anything about Iowa weather, and your zone, I cannt offer any help.

To grow luffa, you need a long growing season for luffa to become fully grown and ripen(about 5 months from frost to frost)