There actually is ABDL clothing available to men, you just have to know where to look.
On Etsy, there are sellers who makes custom clothing for ABDLs, men included.
You can also find on Etsy various kid-friendly clothing that is also made in adult sizes.
BiggBabyBoutique has been quite good for me in the past many years ago.
Ebay can sometimes have ABDL-friendly clothing.
starryideas.net also makes custom ABDL clothing, and has produced some high quality clothing. If you're willing to pay a higher price, the results are very good, and tailored to what you want.
You can also find ABDL men's clothing with the various ABDL diaper sellers out there, like Rearz.
And if none of that works for you, if you're on the smaller side a boy's XXL/XL may fit you - and you can find some really cute clothing in those sizes from regular clothing stores like Children's Place or Wal-Mart.
I hope that helps