Sorry I can't offer much help. Most mushrooms are harmless to plants, but certainly not all (some of the Armillarias come to mind). Any chance of pictures? Also, keep us updated if you can.

If you can provide samples and enough info, you might get some suggestions from the local ag extension office.

Here is a link that might be useful: Putnam County Ag Extension Office

Here is a picture of the problem mushrooms.

Yesterday I tried an experiment. I went through about 70 of the mini vinca plantings and either dug up and replaced the soil if the plant was in bad shape, or simply took about a half inch of soil off the top of any plants that showed new growth and otherwise looked ok. I marked those that used the second method and none of them had the mushrooms this morning, although with the weather conditions last night, there was not a lot of mushroom activity this morning, so at this point my experiment is inconclusive.
My theory here is this:
When I orginally planted, I drilled a hole in the clay that was about three inches wide, put some of a half topsoil/half mushroom compost mixture in the bottom. Holding the plant and root system upright, I added more of my mixture around the sides and then a layer of the mixture on top surrounding the plant. This is what I took off yesterday. My theory is that I have taken the concentrated area at the top. Yes, there is still some around the edge of the roots and underneath, but I eliminated a good portion of it without having to dig everything up and replant. I will know better in a couple of days.
I still would like to know if anyone has any ideas to kill the mushroom spores/fungus without killing my plants.
Thanks for any help,
Cliff