I’ve replaced clasp springs in the older style SMP bracelets (models 2531.80, 2254.50 etc). Genuine OEM clasp springs were available from Cousins at the time, and from eBay for around £15.
It’s an easy enough job on those bracelets; I did some minor dismantling of the clasp mechanism beforehand to access the spring and therefore gain confidence that I’d diagnosed the problem correctly.