So I deleted my RTK keyword to Kanji deck the other day because it was getting to be too much of a pain in the ass to keep doing it. Mostly because I keep forgetting the key words. That said, I don't want to give up writing the Kanji, as I have aspirations to maybe pass the Kanken test someday.

Then I realized, I have a copy of Heisig's RTK 2 4th Edition which has a Japanese sample word for each of the Kanji and groups them by their phonetic radicals, allowing you to see the phonetic patterns in the kanji. So I got to thinking, wouldn't it be great if there was a deck that was kana->kanji (only target character(s) in kana) and based on Heisig's oft ignored 2nd book. It would be a great way to kill 2 birds with one stone. First, you're solidifying your knowledge of each Kanji's on-reading, and connecting it to a real japanese word that uses the kanji (not ambiguous like Heisig's keywords). Secondly, you're maintaining you writing ability.

There is one small problem, which is the 4th chapter of Heisig 2 lists Kanji with no on reading and provides no word, but for those kanji you could just attach the kun-yomi word that best matches Heisig's definition from book 1.

So I guess I'm just wondering. Is there already a deck like this out there? Or would it have to be made?

There is a Japanese keyword project, but maybe not quite what you want since it favours kun-yomi words and puts the whole word in kana.
https://sites.google.com/site/wrightak2/afterrtk1