I know this is not an optimal method, but I did a full text search on デジタル大辞泉 with
五段化, and found the following examples of ichidan-to-godan change.
- 湿気る: 下一段動詞「しけ（湿気）る」の五段化。
- 下さる: 《動詞「くだされる」（下一）の五段化》
- 抉る: 《「こじる」（上一）の五段化》
- 遣わさる: ［動ラ五（四）］「つかわされる」（下一段）の五段化。
下さる and 抉る are always godan in modern Japanese. I didn't know 遣わさ(れ)る can conjugate as a godan verb. I did a similar search on 明鏡国語辞典 and 湿気る was the only verb with the remark "五段にも活用". So I think 湿気る is a rare example of verbs that are both fully godan and fully ichidan in modern Japanese.
FWIW, I think I usually use the godan version of 湿気る. Most similar slangy verbs made from an on-yomi noun usually conjugate as a godan verb (駄弁る, 事故る, 愚痴る, ...), so the ichidan version may become less popular in the far future. This question may be related.