My mom has diabetes too and i did some research for her insurance companies. Yes, there are companies that has insurance coverage for visitors with pre-existing conditions but will be higher. In my mom's case, it was some where around $250-$300. Definitely its gonna be higher but its up to you to decide if its worth it or not. I hope it helps. Follow the link below:
  http://lmgtfy.com/?q=health+insurance+for+visitors+with+pre-existing+conditions