Great knives !
It seems the solo alox used to have a bail. The rear rivet seems to have the holes for the bail. You could write an email to Victorinox and ask them if they could send you a replacement bail. If you do, you could attach a foto of the knife and tell them it`s a model solo, so they know it`s a 1-layer knife. The bails for more-layer knives are wider.
It worked for me once...