Transamerica, Prudential, or American General are your best bets.
to correct my earlier post, Transamerica will not insure him if he was diagnosed with type 1 diabetes before age 45. So, if it was truly "juvenile diabetes" (meaning he was diagnosed as a child), then Pru or AmGen are best bet.
But, we really need to know his exact a1c readings over the past 12 to 24 months and his height/weight over the same time period.