World-renowned Paspaley Pearls were kind enough to reply to my enquiry about Mother Of Pearl as used as inlays in Martin guitars amongst others. For your interest, here is the information received from Purchasing and Sales followed by a link to a video from the company's official website. Enjoy!
"Thank you for your enquiry on Paspaley Mother of Pearl.
Each year Paspaley produce a commercial quantity of MOP (approx. 300 tonne), as a by product of the Pearling industry. The bulk of this production is exported to a number of customers who predominantly manufacture blanks for producing buttons for the fashion industry.
Some of those customers also specialise in producing MOP sheets / blanks suitable for use as inlays in furniture / musical instruments. One customer specifically manufactures the MOP that is exported to the US and is used by Martin Guitars.
We have approx. 8 grades of MOP that are available for sale. Customers do purchase different grades dependant on their use. They also use different parts of the shell for different products. Generally, the higher quality of the finished product, the higher grade of MOP that is used.
I would only be having a guess regarding quantity of MOP that is used for Guitar inlays. I will contact my customer and enquire as to the quantities that he produces for Martin Guitars."
http://www.paspaley.com/#/content/quest!video
http://www.paspaleygroup.com/eng/index.htm