If you are not in Santo Domingo (quite a few places to pick this kind of thing up) then I suggest walking onto a working site and asking the foreman, I?m sure he will sell you one or point you in the direction of the nearest place he will make some commission for the sale.
if you are not successful in renting one, you can buy at OchoA in Santiago a Bosch Jackhammer for about 28,000 pesos.
You might want to try Jerry (i don't have his number handy but he is in Adscene as well). He has heavy equipment but also rent smaller machines. He is located across Puerto Chiquito after Sosua abajo.