would I be able to get my medication reliably?

You should first inquire about that with your medical team back in the States.  They may know, or will be able to find out since that is their job.  Or perhaps inquire with the Medical schools in San Jose.  Good Luck.

There is a courier service that brings things from Doral, FL to Heredia for $6.00 per pound. They bring medications all the time. From Heredia, there are a couple ways to get your meds (or whatever) to you in Costa Rica.

The question of whether or not your Genvoya is available here is a little thornier. Outside the CAJA system, all wholesale importation of medications is based upon the importer's determination that a profitable market exists and upon the Ministry of Health's determination that the medication is eligible to be imported. Some meds suddenly appear and others just as suddenly disappear. You never know. So continuing to rely on a U.S. source is probably a good idea. Get them to "perscribe" a double dose, i.e., a 180 day supply and proceed from there.

What medications are available within the CAJA system is another matter altogether. There, there are significant budget constraints and, as in the public sector, there must be enough of a demand to warrant adding a medication to their formulary. And again, meds can appear and disappear at any time.

In the CAJA, medications for some conditions are significantly limited. For example, the last time I checked, Type II diabetics who are insulin-dependent were given only short-acting insulin, only one syringe and needle per day, and no at home testing supplies whatsoever. Likewise, they only offered one medication to control high cholesterol although some meds don't work for some patients. You see where this is going . . .