In the grand scheme of things, I can think of better ways that Indonesia could contribute to the Pacific Islands Forum than some 12.7 mm HMG's. And by better, I mean contributions which are both more efficient and more meaningful.
Looking at the Pacific-class patrol boat operators, they are operated by a mixed bag of naval/defence and police services. As a result, the patrol boats do not have a standard armament with some being (or perhaps have been) armed with a 20 mm gun, while others are unarmed, and still others being armed somewhere in between with either 7.62 mm or 12.7 mm machine guns. I would guestimate that half or slightly more (12 out of 22) are unarmed since they are operated by police services. As the replacement patrol boats start getting commissioned, I would anticipate that trend would continue.
One of the impressions I have gotten is that any armaments kitted out aboard current Pacific-class patrol boats will be drawn forward by their users into the replacement vessel(s). So I do not anticipate much 'demand' for guns to arm the 19 replacement vessels. Relating to that, if Indonesia were to source machine guns for Pacific Island Forum members, unless the guns were sent to Australia to be fitted aboard the patrol boats prior to their departure from Australia then I would expect a significant percentage of the cost of Indonesia's contribution to come from the cost of shipping. As a matter or practicality, I do not imagine that there is significant direct shipping between Indonesia and places like Kiribati, the Cook Islands, or Tonga.
What I suspect would provide a more meaningful contribution would be for Indonesia to provide either funding grants to help purchase fuel and operate the patrol boats, and/or provide training slots that Pacific Island Forum members could send personnel to Indonesia to develop relevant skills. Another option would be for Indonesia to provide small detachments to help the Forum members maintain and operate their patrol boats effectively.
From my POV, the Pacific Island Forum members which would likely need the most assistance to operate their patrol boats are also most likely the ones which would be least assisted by military aid from Indonesia, as opposed to foreign (non-military) aid. At approximately USD$12,000 per M2, to provide a machine gun to each patrol boat likely to be kitted out by their user would likely cost about USD$110,000, plus whatever the shipping costs to the different islands would be, and some nations would likely not benefit since they most likely would not arm their patrol boats (at least not to such a degree). OTOH if Indonesia were to instead providing up to USD$12,000 in funding to purchase fuel for operations or something else similar, then I suspect such contributions (which are not automatically military in nature) would be well received.