Not through any legitimate source, no.
CS5.5 is no longer distributed though authorized sources as far as I know, certainly not through Adobe. You might find an old copy hanging around someplace, but be very wary -- most such offers are either counterfeit or not transferable.
Are you aware that if you have one licence only one user can use it at the same time? It is only allowed to install it and activate it on 2 different computers.
If you have a single serial you have to buy anyway another one for the second coworker.