Hi,
I too agree with foobar.
I am assuming, as you say you have a croft, that you are in the northern half of Scotland, because of this I think you may struggle to find sheep to buy for fattening, during the summer months, as most lambs will not have been weaned then, unless you have some farmers who lamb really early, but I would think most of the lambs from them would have been sold as fat lambs in the spring or early summer. From september onwards is the traditional time for store lamb sales, which isn't much help to you if don't want them through winter.
As for breed, as foobar says, go with what is available local to you.
Regards,
Sue