There is a long discussion about this somewhere on this forum.
I use a home sewing machine. It's perfect. http://www.sailmakerssupply.com
Get the needles, the v92 thread, and seam stick tape. The seam stick tape is the secret. Once put in the seam, your repair is solid. Get 1 yard of dacron to make patches which you put inside the bladder. You can get matching nylon canopy material at sport kite shops. It's not polyester, so don't do big repairs with it. I leave the bladde in when I do repairs. It's easy to push the bladder out of the way and keep track of where it is when sewing.