From Ljubljana; Pick up the 104 at Stožice Stadium and follow it north and past Trzin and Mengeš. Then take the 225 which will bring you all the way up to Kamnik. From Austria, take the E61 past Jesenice, or the E652 through Podljubelj, both following signs for Ljubljana. Journey time both ways is approximately 45 minutes after crossing the respective borders. From Bled it's an easy 50 km journey following the E61, turn off at Vodice and follow the signs for Kamnik.
For those with electric cars, there are a few charging stations around Kamnik, see here for more details.