I would have to check, but at the recently opened Sirena super market there is a little GNC booth... actually it's a small version of the store. I would not be surprised to see them carrying Glucosamine-Condrointin and even GSM complexes.
If all fails, there's always ebay and having it shipped here thru a Miami based forwarding service. Can be cheaper than buying locally too.
Glucosamine tablets or capsules you can get - in Puerto Plata, from natural products shop opposite Discount Farmacia on 12 de Julio (at crest of hill just as it descends towards Post Office). What is much harder to get is glucosamine powder - JD, bless him, just brought me in 1000 grams from his US trip.
The mini GNC booth at Sirena has it, but it's over priced.
I buy my monthly supply of a Glucosamine/Condointin/MSM compound on e-bay for USD 9.99 (including shipping to MIA) plus USD 3.00 per Lbs. shipping down here, which cover about three one month supplies... so, it comes to 10.99 (RD$ 390.oo) a month.
I grow fingernails like a tiger, my tendons don't hurt anymore, even when abused by excercise and my knees have gone silent.