If you are going to be travelling in July, then you need to book accomodation in advance, it's peak tourist season anyway, but Scottish schools are also on holiday and a lot of us holiday in our own country !
http://www.visitscotland.com/ can help you with accommodation. I would even phone them and get them to help you. They charge £4 booking fee for ALL the accommodation you book, not per place and are most helpful. They actually phone the B&B whilst you are on the line and tell you then and there if there is space and then email you all the details.
I used them for a road trip around Scotland at the last minute and they booked 7 nights accommo for me all over in about 20 minutes which is far faster than I could have organised it and as she was suggesting the places, I would google them as I spoke to her to check that they looked ok.
Have a good time !