I guess that first you'd need to compare the measurements of the pattern and the measurements for the size needed. Will it need shaping to accommodate an adult's body? It could be quite complicated, or if it's a simple pattern it could be fairly easy. If you have the name of the pattern and the book it's in, someone might have it. Alternatively you could find a similar pattern in the correct size. www.ravelry.com
is my first place to look for patterns.