Online Clothing Stores:
Almost any store is an online clothing store! But i hope i helped a little and sorry about the prices, i have expensive taste
you should use silkscreen fabric ink. Do not use acrylic paint it will dry in the screen and ruin it. You can buy the silkscreen fabric ink in art supply stores. after you silkscreen the shirts use a hair dryer to heat set the ink and make it permanent Strange enough you can also silkscreen with soft scrub (the one with bleach) it will bleach the area of the shirt a light color and it looks pretty cool, but make sure to wash the shirt before you wear it!