Like "a lot of," the singular noun phrase "a handful of" has the notional force of a plural determiner when it's used with plural nouns, even though it's singular in form.
In the existential construction "there is/are," "a handful of" usually takes a plural form of BE (all examples from Google):
"” There are millions of competent writers out there. There are hundreds of thousands of good writers in the world, and there are a handful of great writers. (45,300 citations)
The singular form is also correct, but not nearly so frequent:
"” MÃ¡laga's peripheries are commonplace concrete, but its pulsing centre retains the feel and swagger of its history. There's a handful of impressive monuments and some charmingly dilapidated old streets. (3550 citations)
The noun "handful" hasn't achieved the status of "lot" in "a lot of," which is now considered a plural quantifier, so, being singular, it can take a singular verb:
"” While the job seems easy enough, a handful of variables is thrown into the game including a drug cartel boss (Willem Dafoe), his American right-hand man (Mickey Rourke) and an ex-FBI agent (Ruben Blades) eager to get his hands wet in the bloody feud
"” A handful of cases has also been identified in Europe, with suspected victims in Britain, Germany, Italy, Ireland, Switzerland, Romania and France.
But much more often it takes a plural verb:
"” In some classes, only a handful of students are sprinkled among the many desks, and teachers have more time to address individual concerns or questions.
"” A handful of students are doing the best they can to make sure the rest of the student body is registered to vote in the upcoming elections.
"” NEC Corp. has created a network linking classrooms at the University of Wisconsin in Madison and Keio University near Tokyo. A handful of students do not even set foot inside either classroom, participating in the lectures with experimental portable video phones connected via wireless broadband links.
The choice of verb number in the "there" + BE construction also depends on the level of formality. Informal speech and writing accept "there is" with plural nouns, while more formal writing favors a plural verb. The example sentence looks like informal business writing, in which case either form would be acceptable.