Actually, I don’t exactly like the idea of introducing the Kanji to sentences after they have been learned. Vocabularies might be taken consideration of to some extent, but I generally disagree too (for the sake of technical difficulties).
With tools, it matters much less whether Kanji are learned or not.
At least I expect sentences to be translatable, and read correctly, with an aid of tools, like Yomichan or https://ichi.moe. (Or at least on par with Wikipedia / Japanese websites, which of course sentence level parsing, like ichi.moe, is error prone.)
IIRC, it’s only a problem for first 10 levels. (Readable for later-on learners and natives, but difficult for newcomers, even with tools.)
^ Yeah, the Romaji here is wrong, and I don’t think there are tools that can help.
Truthfully, example sentences shouldn’t be just automatically generated. They should be proofread too. And that’s pretty much the problem with Anime Context Sentence script. (On searching accuracy, and sometimes no results, even if there are.)
In the end, example sentences generally can be found in Goo, Weblio, ALC, or perhaps simply, Google. For the sake of convenience and reliability, probably try [Userscript] WaniKani JJ External Definition from Weblio (JP) and Kanjipedia