Congratulations! You have chosen a really great destination for your holidays!
You can find B&Bs not only in almost every little village but also in very remote regions. There it´s particularly the farm houses who are offering inexpensive but excellent accommodation. Just look for "B&B" signs on the road and I guarantee you you will have success. Before I bought 20 acres of Scotland I had visited this charming country many times and there was only one reason why I had to drive 3 hours to find a free room. It was on the first Saturday in September and the evening after the famous Braemar Gathering ...
Beside this I really NEVER had any problems but if you travel in July or August I nevertheless give you the good advise to look for a B&B in time (from 3 or 4 pm).
you really cannot find a B&B you don´t have to worry. There are
enough other accommodations like the more expensive hotels,
a lot of cottages
and the numerous well-equipped camping
In the main saison I think it would be better to stay two or three nights in a B&B making day trips from there. There are so many things to do and to see that you could visit marvellous castles and palaces or unforgettable view points even on foot! If you prefer to explore a region and discover its timeless beauty this is the best you can do.