Hiya,
I have not done this but off the top of my head (is he in the States or UK?) I can suggest using PayPal to swap money perhaps between UK-US bank accounts (I do this for various transfers; loan payments, phone payments, any others back in the US. Costs <$1 PayPal fees versus bank wire fees) and purchase the card from any providers online to then have it shipped to him, or maybe ask a friend or relative to purchase the card on your behalf and sort payment via that method to him. Thinking about it now, I am not sure if these type of things will ship.
Otherwise, I often just purchase amazon gift cards as a solution for family and friends back in the states. Perhaps the reasoning behind you not being able to here is the lack of chip/pin cards in the US, hence no availability for purchase or use here.
Hope that helps a bit!
Lauren