Is there a list of sympatric orchids that live with Darts in nature?

All I can recommend is finding Orchid species that come from the same country as your frogs and checking with orchidspecies.com to see what part of the country and what elevation they are found at. For example, pretend your frog of choice is Ranitomeya imitator (any of the locales). You would search for Peruvian species of orchids, and search the species on orchidspecies.com. Orchidspecies.com will tell you what the climate and elevation they are found at, as well as what region of the country (sometimes). In the case of Ranitomeya imitator, they are found in lowlands and montane forests of up to 950m in elevation (according to dendrobates.org). The orchids you would search for would have to be below this elevation. I suppose to make it even more likely that you will find a sympatric species you could look at the elevation of certain locales where the frogs are found such as Cainarachi Valley. While I can't tell how accurate it'll be simply because there are many locales where the frogs are from, I can tell you that you will be much more probable to find a sympatric orchid species with the above information than without it.

I know that there are a lot of very knowledgeable users on this board that know a lot more about biotopic matters (such as this) than I do. Hopefully they can chime in and help you out more than I could.