Yes you are right most of the water is privately owned. There are some association/public water but this is not free. I fish the Beauly,Brora, Connon, Deveron, Ness, and Spey. You will recognise the last two as everyone in the states seem to be well up on Grant the Wizzard of the Ness. The Deveron is a neighbour of the Spey 20 miles to the east. The Beauly Connon and Brora are all north of Inverness the first two are Hydro electric dammed rivers and are timeshare. The Brora is a classic highland river.
The Deveron enters the sea at my home town of Banff and I am lucky enough to rent a private stretch for the entire season. It is just a short length and unfortunately single bank. But it is very pleasent to be able to go up fishing anytime I feel like it.
Both the Ness and the Spey have excellent associatin water, which although not free are excellent value for money.