I will be happy to help out editing your copy or marketing collateral, if you don't already have that covered. Just drop me a line when you come to fleshing out your website.
Give the tat artists some of the shirts. They like to show off the artwork that they have done and people waiting in a tat shop usually skim through the tat book, look on the wall at the designs and just try to distract themselves to kill time, seeing the shirt would likely have a better impact while they are in that environment over say a facebook post or a website ad. Easy way to get free advertisement that targets people interested in the artist. The fact they are tat designs adds its own gimmick which will bode well with the tat addicts that go there (some people just turn up to chill with the artists).
Will be hard to get it off the ground but its relatively easy to keep on top of.
Good luck to ya bud.
If you intend it to be an online business - check availability of domain names as well.
Something simple?
Inkshirt?
Also, how are you getting around propriety rights?
A good profit can be made in t-shirts if you get some popular / unique designs.
Are you looking to create the t-shirts yourself or outsourcing? A second hand vinyl cutter and heat press will get you going, loads of tats are line art so simple black / white cut vinyl on bold coloured tee's will make for some distinctive wear.
Loads of competition online but selling locally through the tattoo shops could work out quite nicely.