When I needed content along these lines for my project, I found that the easiest way to find it, was on pixiv. You'll need an account for this.
First, go to pixiv, and find "user settings". It should be on the upper right, although you can also get there a couple of other ways.
Then, when you're in user settings, either tell pixiv that you're under 18, or just tell them to hide adult content. Either way, you'll get the same effect, and don't worry, you can turn it back on later.
Now, comes the trickier part. "straight shota" is our word. It's english. The japanese call this stuff "oneshota". So you have to search for that. Now, I did the heavy lifting already, and found that the term in hiragana/kanji is " おねショタ ". If you need to transliterate something else, though, you can go to google translate, tell it to go from japanese to english, and whatever you type, will be transliterated in a "did you mean" box.
Finally, ignore the shit in the yellow boxes. You don't need to get pixiv premium to see that stuff, it's just an ad. You'll find those same pictures, sans paywall, further down in the list.
so tl;dr, go to pixiv, and search for おねショタ with your family filter on.