Interesting search - boy little clothes - instead of little boy clothes.
Not being critical - just wonder how the internet search engines are going to handle this or if the result will be the same either way.
Yes this forum treats this description differently than what the usual
ordinary would be.
Fascinatingly adults do not fit into little children's clothing but they do fit into 'LITTLE' clothing designed for adult wear and some of these are down right cute making the case for wearing such !
Thus to answer your question - search here and there on this forum and then venture over to eBay or Etsy.
On eBay possible to find a seller that does custom work - be careful of custom Asian work - the sizing is critical - make sure you are dealing in the same increments of measurement.
Wearing boy little clothing can be a conversation starter just like I have commented on this sentence structure.
Yeah - you can find clothes for adults that would reasonably pass as something a little boy would wear pretty easily. Cartoon t-shirts for men are readily available at Walmart or nearly any other department store. Like dogboy mentioned, overalls are another option I personally dig, although I admit the look is probably a bit dated as I seldom see boys wearing them nowadays. Another option to spice up plain clothes is with appliques.
If you happen to live somewhere that has a Forever 21 store you might want to try looking there. I've bought some really cute overalls and even shortalls in the men's section. My favorite little boy outfits usually involve overalls and shortalls over onesies or shirts with cute designs on them.