Production on these was stopped years ago leaving the popular 1.1mm Stub as the only one available from TWSBI.
I found a vendor in Germany and one outfit in Texas that has both the TWSBI Classic Mini (black) and replacement nib sections for the Mini and the Diamond 580 available in the 1.5mm. I bought one Mini and one replacement section for a 580. I think the replacement sections fit both the Standard and the AL versions of both the full size and mini. But it doesn’t fit the VAC or the ECO, etc.
I found a vendor in Germany and one outfit in Texas that has both the TWSBI Classic Mini (black) and replacement nib sections for the Mini and the Diamond 580 available in the 1.5mm. I bought one Mini and one replacement section for a 580. I think the replacement sections fit both the Standard and the AL versions of both the full size and mini. But it doesn’t fit the VAC or the ECO, etc.