Gauni - N/N class
gauni yangu - my gown
gauni zangu - my gowns
gauni ya Rehema - Rehema's gown
gauni za Rehema - Rehema's gowns
gauni za dukani - store gowns
However I also found gauni as part of Ji/Ma class
gauni /magauni (gauni langu/ magauni yangu
gauni la Rehema - Rehema's gown
gauni ya Rehema - Rehema's gowns
gauni la kijani - green gown
magauni ya kitenge - dresses of printed material)
Any insight from a native speaker ???
I'm not a native speaker, but I know that many loanwords are in flux between assignment to the N/N or Ji/Ma class (so you might find either class given in a dictionary entry). Here's the background:
This class was originally used for foreign loanwords because the singular did not necessarily have a prefix, but such words are usually placed in the N class now, although they are often given Ma class concords and the ma- plural by many speakers.
Borrowings referring to people are still habitually placed in the Ma class because of animacy concerns. There are a few words in the U class that take a Ma class plural, and some N class words that may take a Ma class plural to indicate a collective grouping.