Hi Dan,
i've found it.... through my broken understanding of Cantonese/Mandarin, the user on Instagram stated that he bought it from Taobao (china's equivalent of eBay)
Here's a link to what i've searched on TaoBao.
http://item.taobao.com/item.htm?spm=a230r.1.14.55.DVjeGw&id=38915871578&ns=1&abbucket=12#detail
Here's another version:
http://item.taobao.com/item.htm?spm=a230r.1.14.41.DVjeGw&id=42999710192&ns=1&abbucket=12#detail
What you would like to type in the search box is: 边线器
Which translates to (Literal translation) 'Side Line Tool' and is pronounced as Bien Sian Ji.
I've not bought from TaoBao before but perhaps i may give it a try and see how it goes.
Cheers,
Frederick
Update: 押捻 in the first link is the one you are looking for, it comes in 2.0mm, 2.5mm, 3.0mm, 4.0mm and 5.0mm.
押 (Pronounced as "Ya") is to ''PRESS'' down, and as you would know the next would be the double pronged version which is under 溝捻
溝 (Pronounced as "Neah") is to "Pinch".
If there's anything else, feel free to ask.
Happy crafting!