If the chlorine has any Stabilizer (Cyanuric Acid) you cannot be using that with Bromine. If the chlorine is unstabilized then go to town.
Yes you can find granular Bromine out there.
Bromine is not affected by stabilizer (cyanuric acid) so there is no problem using stabilized chlorine to oxidize bromide to bromine. As for granular bromine, there is brominating concentrate that is a combination of Dichlor with sodium bromide so produces more bromine, but unless you've initially created at least some bromide bank such a product will produce a little bromine with a lot of chlorine. The same is true for BCDMH tabs that are really a combination of both bromine and chlorine -- without a bromide bank initially, they will produce both bromine and chlorine, not bromine alone. Of course, over time a bromide bank is built up as bromine is used/consumed.
So if one wants only bromine then one initially adds sodium bromide to the water to create a bromide bank. Then, any oxidizer added such as Dichlor, bleach, MPS, or any bromine tabs used or any brominating concentrate will all create bromine.