I don't know of a textmate plugin, but I'm pretty sure it does this already via Edit → Spelling, which is enabled by default for comments. Start by checking that you don't have this turned off for comments, or set to the wrong language.
It's unlikely that someone will develop a custom plugin to do something that textmate already has as a feature.
BTW, the //Retrns example you give above is joined to the two slashes. No word in the dictionary has two slashes at the start, so it may be missing it for this reason. If this is the problem, file a bug report with the textmate guys, or perhaps consider moving to a more feature-rich editor if it bothers you a lot (PHPStorm picks up that typo just fine, and you can also check the names of variables and functions if you want to be really pernickety).