According to the Cambridge Dictionary, availability is uncountable. That's not the end of the story, though: according to this NGram, usage of availabilities is not unusual, although mainly in technical writing. Here is an example:
Past feeding ecology studies of shorebirds primarily focused on food selection patterns and availabilities from single stopover sites. Ecology and management of migrant shorebirds in the playas
The sentence talks about assessment of food availability at several sites. He chooses to refer to the assessment for each site as an availability, and there is one for each site so there are several availabilities. This writer (and many others) think that availability is countable.
The countable/uncountable entry in a dictionary can be a useful guide, but if it says uncountable and you really need a plural, go ahead and make a plural.