Orphaned kittens

We live in the country in northwest Indiana, very small, depressed
area, we moved here last fall.
A stray cat showed up and gave birth to five kittens somewhere on our
property. We discovered them when their eyes were open, and she moved
them to our dilapidated barn.

This week Mama Cat was hit and killed by a car.
We've been feeding the babies a home-made formula we found on the
internet, and I think they are doing alright, but I'd like them to do
better. We cannot afford a vet for these babies, and I don't feel
good about the county shelter. How would we find out about any rescue
groups in our area? I have scant faith that there is such a group,
but I could be wrong. There is not a pet store in either of the
nearest towns (15 and 20 minutes away). Meanwhile, what else should
we be doing?

I've searched your archives and found another formula that looked
pretty good (1999/07/21 by Lani Scott), and that thread had a lot of
useful information.

Is there more we should know? How do we find out more about how old
the kittens are? They are getting teeth, their eyes are open but dark
blue. They walk, albeit a little shakily. They climb out of their
box.

Kanga