My previous character was roleplayed as a clone that wasn't of another player or the Republic clones. It's pretty common in general for people to roleplay as clones. Is there a reason you're looking specifically for Republic clone roleplayers, though?
I've encountered and dealt with NPCs who were Republic Clones, but no PCs as of yet. Doesn't help that due to their implants and programming, they'd be hardwired into service with the GE, the 'rightful' Republic, and are conditioned to act and look a very, very specific way. When you're playing a role for years on end, it's understandable that this wouldn't appeal to that many people.
Also, you have to remember that most republic clones went through an accelerated growth. By the time it is in Combine, most if not all are dead. We diverge from the canon timeline around year 0 (of course with names before that more appropriately fitting our setting, and probably some finer details since we lack the Skywalker family line). At around that point in time in the canon universe, pretty much every clone trooper had died.