"confederate of" is correct and usable in written English.
You might use it to refer to people who are in an alliance with one another and thereby connected to each other, such as in the phrase, "The confederate of countries agreed to a truce."
The sinister sense of deceptiveness was then transferred, according to a 1914 slang lexicon, to "a female confederate" of "genteel grafters".
In one study, each subject was asked to write an essay that was then criticized by a partner, really a confederate of the researchers.
Moroccan officials say he met several times that year with Abu Musab al-Zarqawi, a confederate of Osama bin Laden who, antiterrorism officials say, is behind a series of attacks.
Minutes after Mr. Karzai concluded his speech, a second, larger explosion rocked the jirga tent, and the session was suspended for 90 minutes as the police battled the insurgents, killing two suicide bombers and arresting a confederate of theirs.
But the region was beset with many disorderly gangs escaped from China, including the Black Flags, who were under the command of Liu Yung-fu, a confederate of the Taiping.
As for Lodovico -- a banished count in love with the virtuous Isabella and a confederate of Francisco de Medici's in the denouement -- his character is too peripheral to qualify as the title figure.
After the battles of Fort Henry and Fort Donelson, the Union began to collect a large number of Confederate prisoners of war.
His customers are mostly groups like Sons of Confederate Veterans, of which he said he is a member.
In 1865, President Andrew Johnson gave blanket amnesty to many of the leaders of the Confederate States of America.
Inflation predicted the defeat of the Confederate States of America long before the victories of the Union Armies.
There were 43 major battles within 30 miles of Richmond, Va., the capital of the Confederate States of America.
