I did a buildout of offices about 6 years ago. I specified that I wanted 5/8" greenboard (the type of sheetrock normally used in bathrooms, with more moisture and also a longer burn-through time) and the engineer couldn't find it.
He looked for 1/2" sheetrock, and couldn't find it in Santo Domingo.
He did find 3/8" ( 3/8 !!!!!!) and used that. I felt as if the paint was thicker than the sheetrock. It sure looked real, but it really wasn't.
Check the large building material suppliers like Americana, Ochoa, or along Ave Luperon in Santo Domingo. Maybe things have changed by now, oir maybe you will need to bring it in.