The phrase "a cavalry of" is correct and usable in written English.
It can be used to describe a large group or multitude of people or things, often in a metaphorical sense, suggesting a sense of urgency or overwhelming presence.
Example: "As the deadline approached, a cavalry of volunteers rushed in to help complete the project."
Alternatives: "a swarm of" or "a legion of".
(Within a few days, a cavalry of mounted protesters had gathered outside the shop).
Before taking any actions, the banks are first seeking guidance from a cavalry of lawyers.
Native Americans would put their ears to the ground to hear or feel vibrations of, say, a train coming, or a cavalry of soldiers on horseback.
The so-called Convoy – a cavalry of hippies, anarchists and crusties that moved around the country from festival to festival – became the focus of the secular authorities' displeasure.
Massive columns and grand arches; stolid steles and glowering busts; eagles and angels and a cavalry of horses in a state of perpetual alarm.
A letter by Richard Doyle to his father shows this 19-year-old Punch illustrator overwhelmed by a cavalry of drawn characters clamoring for his attention.
In connection with a document there was some discussion of a cavalry brigade of the SS.
All who have seen them play, who have thrilled to an attacking style at once so spirited and so cuttingly precise that the effect is of a cavalry charge of surgeons, must share that belief.
At the Battle of Austerlitz and the Battle of Jena-Auerstadt, he commanded a cavalry brigade of carabiniers in Étienne Marie Antoine Champion de Nansouty's First Division.
Approximately the same number of trains (about 40) were required to transport a cavalry division of 4,000 as to transport an infantry division of 16,000.
The painting of World War I made a cavalry attack of Hungarian hussars look like a Sunday outing in the country rather than a bloodbath.
