I always cut my own fletchings from full length feathers. Not sure how far you've got, but for what it's worth, I'll run through how I go about it.
1. I work out exactly what shape and measurements I want my fletchings (I usually use 6.5" by 3/4" medieval style triangles, with a trailing edge)
2. If I'm using complete feathers instead of pre-ground, I insert a razor blade in the thick end of the quill, and start a small cut. I then either tug the two sides apart so it splits down the length, or run the blade all the way through the quill to the tip.
3. The bad side is discarded or used for something else, and the quill of the good part is now ground. To do this, I place the feather in my fletching jig (which I made using bits of offcut wood and two brass sheets I got from B&Q glued to 2 bulldog clips) so that the quill part is exposed. I use sandpaper to bring the quill down as small as I possibly can.
4. I then take a long piece of wide masking tape (you can get this at most places) and carefully stick the feather to it lengthwise, making sure the quill is as straight as possible, otherwise any design that is cut out will change as the quill straightens against the arrow shaft.
5. I turn the feather and tape over, so the adhesive side is facing down, and stick it to my desk/table. The feather is now sandwiched between desktop and masking tape. I use a ruler and pencil to draw my design on the non-adhesive side of the tape, then pull up the feather and tape.
6. Using sharp scissors I cut along the lines of the drawing and finally pull the tape off the feather making sure I pull it from thick end of the quill to thin end to avoid ruining the feather.
This is a lot of work obviously (I love doing it, and will happily sit and ignore my girlfriend for hours while I plough through 30 odd fletchings at a time. She loves it) and the easier option is to buy pre-ground left-wing fletches from somewhere like the longbowshop.com or longbowandarrow.com as it saves a lot of time, and you're guaranteed all left-wing, all nicely ground feathers that you can just get straight on with cutting out.