I am looking for a online vendor for sumi-e brushes. I have two
brushes called 'Das Flow' and 'Happy Dot' and do not remember where I
bought them from.

Findik,
  
The following online vendors sell the "Happy Dot" brush, and a number
of "Flow Brushes" (I was unable to find one specifically called 'Das
Flow') :
  
Oriental Art Supply 
Toll free 800.969.4471 
Phone: 714.969.4470 
Email:info@orientalartsupply.com
  
"H1c: Happy Dot Brush
Tip Dimensions: 3/16" x 7/8"
List Price: $9.00 
  
Description:
An absolute delight. Happy Dot does fine lines and dots with extreme
ease and delicacy. No more split tips. A dream for all artists.
  
General Use:
Wonderful for small scale subjects. Offers smooth delivery of anything
that comes to a point; delicate pine needles, sharp petals, lines,
animal whiskers, calligraphy, signatures, etc."
http://www.orientalartsupply.com/products/brushes_hard.cfm
  
Flow Brushes
http://www.orientalartsupply.com/products/brushes_combination.cfm
  
  
Paragon International Art
Phone: 425-497-9915
Email:info@awesomeartsupply.com
  
"ABD-6DLB2 Happy Dot 	 
Price $6.00 
	  	 	 
Description
Larger among all dotted line brushes. More versatile.
Handle: 6 7/8''; Bristle: 15/16'' L, 1/4'' dia."
http://www.awesomeartsupply.com/product.asp?itemid=1214&catid=356
  
Flow Brushes
http://www.awesomeartsupply.com/view_category.asp?cat=351
  
  
I hope this helps!
  
  
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Search strategy:
sumie-e brushes
brush "happy dot"
oas "happy dot"
"das flow"