I wouldn't mind making a homemade one myself if the method were simple enough.
Even I can tell you how to do that, actually. Just need the following:
-A blank(Or it can have a pattern or whatever if it fits what you want it to look like in the end) shirt for the base
-Picture(s) you'd like put on said shirt
-Transfer Paper(Iron-on is the type I use, not sure if there're other varieties.)
-Printer(Obviously)
-Iron(IRON-on is called such for a reason.)
Print picture on transfer paper(Might need to print it flipped horizontally depending on paper). Follow instructions of transfer paper to apply to shirt using iron. Let cool. Enjoy!
A note: Don't machine-dry a shirt made like this. The picture will probably get all messed up and start to crack after some time.
If I missed anything, someone else who knows the method will hopefully correct me, but I'm pretty sure this is it.