Aran sweaters can be bought in almost any store on the aran islands, off Ireland, near Galway.
But also in many more stores in the whole of Ireland and shops that specialize in Irish things outside Ireland.
Real Aran sweaters are knitted of wool, and are pretty thick.
Therefor they are really warm, if not windproof.
If you wear them in the right climate they will not make you sweat, but not many people live in the right climate.
If you like to own an Aran style sweater, but do not live where it is cold enough, try to buy a thinner copy of man made fibres, those are often less warm.
By the way, the story that the sweaters are linked to clans is not confirmed, it is more likely that the women of a certain village or family did use certain patterns by preference, therefor the men of a village would wear them. But not like Scotland where the tartans are claimed by clans. (Used to be as informal in the past.)
That exact sweater is by Markus Lupfer. You can buy it here but its expensive
However this one looks a lot like it
And if you wanna browse for more similar ones try it here
Hope I helped xx