The phrase "available in theory" is correct and can be used in written English.
It means that something is possible or exists in concept or principle, but may not be practical or readily available in reality. Example: "While renewable energy sources are available in theory, the high costs and limited technology make it difficult for many countries to fully rely on them at the moment."
The findings suggest a distinction between what is available in theory and in practice.
Various legal claims may be available in theory, experts said, among them defamation, infliction of emotional distress and malicious prosecution.
Clicking on that fare yielded a calendar showing me the departure dates for which the fare was available in theory.
That hope alone might convince the ECB to keep support to the banks still available, in theory at least, until the vote.
In cases of tenant eviction, domestic violence, unfair dismissal, denial of social security and public health, they provided remedies that were available in theory but rarely in practice.
Women – in particular the women Keith observes in torturous peripheral vision plunging in and out of the castle's pool, topless (and occasionally bottomless) – are undoubtedly more available in theory, but not, strictly, in his experience, in practice.
And while more jobs may in theory become available to American graduates, they will have been cheated out of the full M.B.A. education.
In the last 3 decades, cytologic screening has —in theory —been available and yet more than 6 million women have died of this preventable disease.
The experts are available 24/7 in theory and the whole thing should take about 5 minutes, according to what it says on the app.
With the recent progress in complete genome sequencing, mining the increasing amount of genomic information available should in theory provide the means to discover new classes of peptides.
end{aligned}Numerous other formulas of this kind are available in sampling theory (Cochran 1977).
