You can google custom tshirts all day long too. If you truly want the advice of a member that has experience, maybe someone will chime in and say, "Yes, I used ABC company and they were really good, blah blah blah."
If not, anyone who would solicit their business here correctly, already has done so by being a preferred vendor. So maybe check out the preferred vendor section and see if they offer shirts along with their products. If you are looking for a custom one that you are designing, I don't know of anyone here who actually does that but they would be wise to message admin first before answering.