Ask Mr. Smarty Plants

Free advice?   Right here!   We have a list of recommended species for Oklahoma.  Each of the plants there can be checked for how well they do in shade and damp conditions.  I also found several previous Mr Smarty Plants answers to questions about erosion control.  Here is a very complete answer to a quite similar question to yours from Tulsa.  This question/answer concerns erosion control on a creekside,  and here are two from Kansas dealing with erosion control and with a hillside in Kansas.

Mr Smarty Plants thinks the answer to the person from Tulsa was both pretty appropriate and complete, so I reviewed those suggestions for the growing conditions for the plants recommended, which can be found in the lower part of the plant record.

Good Choices would include:

Groundcovers - Phlox divaricata (Wild blue phlox) [wet – partial shade], Salvia lyrata (Lyreleaf sage) [sun & wet or dry], and Phyla nodiflora (Texas frogfruit)

Grass or grass-like - Carex texensis (Texas sedge) [part sun & moist], Chasmanthium latifolium (Inland sea oats) [[part shade and shade – moist], and Poa arachnifera (Texas bluegrass) [part shade & moist]

and, of course, Ferns [all of which like shady & moist or wet conditions] - Adiantum pedatum (Northern maidenhair), Argyrochosma dealbata (False cloak fern), Athyrium filix-femina (Common ladyfern), Botrychium virginianum (Rattlesnake fern), and Dryopteris marginalis (Marginal woodfern).

Returning to "Are there any free advice/plants available?"   Free advice is easy, but may be worth what you pay for it [Yours truly excepted of course!]. Free plants is a bit harder, perhaps the best sources for both advice and plants would be either a local plant group or the Oklahoma State Extension.  I found links to the Oklahoma Native Plant Society at the University of Science and Arts or at what appears to be their own webpage.  Here is a larger list of garden groups in Oklahoma.

For the Extension Office, I suspect the Washington County office in Dewey may be closer, but the Osage County office in Pahuska may be preferable to you.