Just a note on the language barrier. I only know a few French words, but quoins is French for corners. Coins in English is hard currency. A coin set would be generally be regarded as a numismatic proof set in English.
With all that said, you probably want a set of CORNER BRACKETS. Check with Greg Mouton, Mouton Music, Crowley, LA. MoutonMusic@aol.com (They check their email about once a month.)