As most of you probably know, the genuine, name-brand replacement leather bands for these makes cost a mint, and they are often odd sizes and shapes, so generic bands won't work. I've found a Taiwanese ebay seller called powerboxwatch that sells generic replacements that are the right sizes for low prices, including some genuine crocodile. Unfortunately they don't seem to keep a large inventory so your particular model may be OOS. But a good deal if they have yours available. Pictured is my Montbanc with the correct-sized 19mm x 17mm band (not genuine crocodile like the original, but at least it fits!) .
The trouble is, certain brands take non-standard size or shape bands (or bracelets) that you just can't find, even at a watch repair store with a huge selection. For example, many Montblanc watches use bands that are 19mm at the lugs and 17mm at the buckle or clasp. 20mm/18mm is a traditional standard size for mens' watch bands (though many today are bigger). 19mm/16mm and 18mm/16mm bands can also be found, but the 19mm/17mm size seems to be unique to Montblanc and is very hard to find. Cartier and several other brands also often require non-standard band sizes and shapes. There are various online sources for some of these, but it takes a lot of searching.