That's different, MV has those types of number plate holders on some of there bikes. https://www.ebay.co.uk/p/PT605B-Riz...Side-arm-Mv-agusta-Rivale-800-2013/2098358340 Looks very similar if that helps with a bit of a modification
Is that what you had planned to fit to your speed triple special? Assume you have a CNC, reverse engineer the one you have, wouldn't take long to draw that in CAD.