If you want to make your own costume from scratch, then the re-enactors markets are good places to buy clothing, or fabric to make your own.
How to make a woman’s shift from the 1600s – a useful video by Elin Abrahamsson. If you have a copy of ‘Clothes of the Common People’ by Stuart Peachy, then this is a very similar pattern, but the video is useful in understanding how to assemble it.