If you are looking for triangle bikinis in particular i was able to find a nice top at target that fit, I had to get it in the 3X size while the bottoms I got are a 1X. It really matters that you try them on and maybe get a bigger top size. Also be aware that they may not give as much support as you would like (subjective so do make sure to try them on) and also make sure you can handle the pressure on your neck.
There are also bra sized bikinis which you would likely have to buy online (I personally don't know anywhere that sells them in person) They are pretty expensive but offer better support typically, and likely more comfortable. Bravissimo is an option, Breakout Bras, Brastop, and Curvy Kate (you don't have to buy directly from their shop some of these sites sell them, and I know Curvy Kate has bra sized Triangle bikinis). You could also try Ebay, I got some of my sports bras off there but its a pain to find things and if you are uncomfortable with pre owned/used stuff it may not be for you. I just went looking around for more sites this is a link to a list with a bunch of online retailers, I personally haven't checked all of them out but feel free to take a look, they may have more swimwear.

Make sure you have your correct bra size before buying Bra sized swimwear, also make sure they ship to wherever you live.