I don't know if you have this on your side of the pond but there is sheepshire or wood sorel plants that can make a nice wine. It is a clover looking green plant that only grows a couple inches tall. Different strains sport white, yellow and purple flowers. They are apart of the Oxalic family of herbs and have a large concentration of oxalis acid. If you have ever had rhubarb then think of crossing rhubarb and young not ripe mulberries with a slight herbal hint on the back end and that is what the green leaves taste like. So look around and if you see any flowering clover then give a single green blade a taste and if sour then you got the stuff.
A simple recipe would be like:
1 gallon recipe
2oz sheepshire flowers
8oz sheepshire leaves (no need to de-stem)
8oz raisins (or possibly one 11.5oz frozen can of Welch's white grape concentrate)
2lb sugar
1 tbs black tea (I like Earl grey)
1 tsp yeast nutrient
1/2 tsp yeast energizer
Yeast (lalvin 71b)
Throw your leaves in a half gallon of water and boil for 15 min. Strain off the water leaving the leaves behind. Combine the flowers, black tea, raisin (or concentrate), sugar and nutrients. Top up with additional water to one gallon. Adjust gravity to what you like. Rehydrate yeast and pitch.
Edit: I originally said 8oz sheepshire leaves based off of memory but looking at some notes and such it is more like 1oz flowers and 2 oz sheepshire leaves. But you get the idea.