I think the DIY option is probably the best option for you at the moment. However, if you are actually obese as opposed to just being a little overweight [yes, there's a difference], then really what you need to focus on is getting healthy rather than where to find clothes.
That being said, find some black T-shirts in your size, and put the names of your fav bands on the back. Find a pair of pants you like, and sew/iron patches on to them. Etc, etc. =)
Hope this helps! ^_^
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