Tons of shops at avenida macabich ....tons. Zara Is ok.
There Is jack and jones
Blanco
A bunch others as well.
Small shops for momento tshirts are actually tan by locals ...with cheesy 5€ to 10€ shirts that you can bring as gifts. They also hace shorts. If you do not mind the label attachment and pretentiousness...common and predictable. Go to the small merchant shops there are other ones at avenida por calle catalán .... Lots of shops run by asians ...chinese with cheap goods that you can use for a couple of days only.
Bit if you go with zara....bleh...might as well. They have good and cheap stuff..the shirt in my prof picture Is from zara. 15€ .