Welcome to Star Trek Answers. What would you like to know? , or Avonos do not offer it, nor have I seen that particular costume piece offered for sale before.  You may be able to find a blue lab coat like it by doing a search through your favorite search engine. 

Find a high quality picture of the lab coat wore by Dr. Crusher & make sure it's what you want before buying.  Ebay, or other sites may have it for sale.  Search for interviews with William Ware Theiss or Robert Blackman, TNG's costume designers & see if it is mentioned, or locate their webpage / email & ask if the lab jacket was custom made or a purchase from a store. Contact Gates McFadden by email & ask her, too.

Also you might check out Star Trek Costume sites w/ the search, Dr. Crusher's Lab Coat.  Memory Alpha shows 2 versions of varying lengths & colors.  Click on the hyperlinks for more information.  TrekFan1984 Ends (talk) 01:09, May 20, 2017 (UTC)

A quick google search turned up this one on Hello Cosplay: (talk) 18:44, May 21, 2017 (UTC)

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