Yamaha made electric start and remote control kits for all 6 and 8 HP 2-strokes from 1984 to 1993. After that, they do not appear to offer any electric start and remote control kits for these motors, which is a real shame.
If you check out Boats.net and Yamaha Outboards for your particular 1999 (6MLHX) Motor, you will not find kits offered. If you check out any 6/8 motor from 1984 to 1993, you will find electric start and remote control kits - and the part numbers - listed in the components sections.
When you click on the part numbers in the components list, scroll down and it will show you which motors the specific part number can be used on - a very helpful feature of this web site.
Unfortunately, I do not know if these older kits can be fitted to your particular motor.