I hate to be a wet blanket BUT if you do not have the ability to produce 1000's of shirts in very short time, you are not going to get into major retailers like Macys, Kohl's, Sears, JC Penny et al.. They want major amounts of products on short notice and you will need a contact at the corporate level. If you don't have a large shop with employees, I do not think you have a change to get in. That does not mean you cannot at some point do it, but if you are just starting out, from a garage or bedroom with limited time, resources ( read $$) you will need to establish yourself locally and see if you can go regional. This will not happen overnight. are you going to do heat press..screen printing...
dtg...sublimation..or..???
There are several threads on the forum about starting and growing your business. Have you read them all? if not you should...there is a lot of info there.
List steps to get my t-shirt designs at major retailers. 
