While answering @Qiangong2's question here: Are Characters customized in different provinces due to dialectal differences? I was looking through the table on 四川方言字.
On the table the following initial keeps showing up:
For instance here is one single entry:
𨈓 | nang¹ | dⁿaŋ˥ | 形 | 瘦小、弱小
The entry for this word in《成都话方言词典》is notated as:
𨈓 [Ĩaŋ⁵⁵] 身体瘦小
《现代汉语方言音库 • 成都话音档》writes it as:
𨈓 naŋ⁵⁵ 瘦小
I've seen both /n/ and /Ĩ/ as an initial, I have a preference of the two, but I have never come across /dⁿ/. I'm guessing that a simplified writing of /dⁿ/ would be: d‘, but how d‘ sounds anything like /n/ or /Ĩ/ is beyond me.