I think multicolour occasionally marks down their 'fine gemstones' tab -- may even be marked down at the moment.
Most sales are adhoc. So kind of have to keep track of them. But right at the moment -- enhoerning, and litnon have both been having sales.
Pretty dependable to find etsy vendors having sales arround mothers day, black friday, cyber monday.
Most coloured stone vendors run sales through Tucson. Which is generally late January to early feburary. Some run sales arround/before/durring the las vegas show. Again both are about moving inventory and create liquidity to buy new stock. Downside of buying at this time is that you end up not having spare cash when they bring their new stock back from the shows (and usually this is the better stuff).