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Andy Banjo used to sell string sets for Mandolin Banjo, which I used on my GH&S, but I believe they have ceased trading:( Clifford Essex also list a set for Mandolin Banjo.

I found this thread in August, when I was looking at another instrument on eBay. 12-string version.
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Just picked up a mandolin from eBay as a restoration project. No label, or other identification, but appears to be the same model. Another Gartini de Lugini?
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Great stuff, very fine sounding instrument. I'm a big Simon Mayor fan and recorded this on My Mandocello a few years back :-)
https://www.youtube.com/watch?v=F8OCZJR_LOI