Quote from gkishot:
Any website that publishes the interest rate would have some delay in updating it.
Especially if you need to use Libor rate which I believe is the case. Since Libor rate I think is not even announced by any body. So what is your definition of 'instanteneous'? Those rates have to be updated on the web once a day at the closing. Unless of course you want to use real-time data by reuters. But this is unnecessary for most purposes.
In fact I am not sure if I should use Libor or other rate.