I have a 29" mountain bike I'm going to put a motor on. I'm going to replace the back wheel with a 26" and my question is about the gears. I need two of them in the same side to freewheel independently one for the motor and one for me to pedal. and I can't find anything online telling me which kind of hub I should use. Can I just use a standard single gear freewheel hub and chuck two freewheel cogs on? I don't want to buy them then be stuck waiting a month for a new hub.
First, if you use a 26" wheel in back, you won't have any brakes as they won't reach (unless you have rear discs).
Second, because you mention that you want a sprocket chain on the left hand side going to the motor, I assume you're going for some kind of off-board solution. These have been really deprecated with the rise in good hub motors as well as mid-drive solutions.
Update: you clarified that you wanted both the motor and the regular chain on the right hand side. As far as I know, there aren't any freewheels that are split so that they can take two chains that freewheel separately. The best you can do in this scenario is to use a regular freewheel and put a one-way bearing on the cog that's on the motor. It'll mean the motor chain will not freewheel -- but it'll also mean the cranks will move when the motor is moving (with the real possibility of breaking your ankles). The safer way is to use a flip-flop hub or disc-brake mount to put the sprockets on the left hand side using either a left-hand freewheel or a one-way on the motor. That way, the bike's freewheel will make sure that you can't break your ankles.
tl;dr It'd be so much easier for you to get a 29" hub motor wheel -- or to keep the current wheel and go mid-drive.
Not an answer to your question about left-hand sprockets so feel free to ignore.