I can't answer about how easy it is to get a gun because I never inquired, but I've seen plenty of Dominican people packing firearms, including the guy at the local colmado with a pistol shoved in his belt.
In general, unless somebody is a member of some police/guard/military, a business owner at his place of business, etc., you won't see people walking around armed.
--I personally don't like the idea of having to buy a gun because everyone else who might become troublesome towards me might carry one. --
Your reasoning doesn't make sense to me. Are you planning on having a gun fight? Are you going to carry a knife because everyone who might become troublesome towards you has one? You are going to defend yourself against a knife with a knife?
Walk away buddy. One doesn't need a gun to cause great bodily harm or death. The same can and is accomplished with plenty of other readily available weapons including machetes, knives, a tire iron, a broken beer bottle, a big rock, a large stick, a big fist, a good boot, or a spiked heel. Even when somebody looses a fight, they might come back with friends and/or weapons. You don't need this kind of trouble.
I've never personally seen a gun used in a personal confrontation, but I've seen the latter items, plenty of times. This applies everywhere, not just the Dominican Republic. It is senseless to worry about who might or might not be carrying a firearm. If someone wants to hurt you, they will find a way. You don't want to get in a fight with someone that feels they have a hell of a lot less than you to loose or just doesn't care. This applies in Europe, America, Canada, and everywhere else.