The "oa" in the word "broad" is pronounced like the words "or" or "awe". In phonetic symbols that is ɔː . However in all other examples I can think of it is pronounced like the "oe" in "toe". Or in phonetic symbols, əʊ . For example, in goat, toast, oat and so on.
Etymology: Common Germanic: Old English brád , identical with Old
Frisian brêd , Old Saxon brêd (Middle Dutch breet -d- , Dutch breed ),
Old High German (Middle High German and modern German) breit , Old
Norse breið-r , (Swedish, Danish bred ), Gothic braiþ-s < Old Germanic
*braido-z : no related words are known even in Germanic, except its own derivatives
Although perhaps not directly relevant to the question, where it makes a difference I am talking about British English pronunciation. So broad is pronounced /brɔːd/ , both or and awe are pronounced /ɔː/, toe is pronounced /təʊ/, goat is pronounced /ɡəʊt/ and so on and so forth.
Best Answer
First we must set aside oar, board etc. (i.e. where the oa is followed by r). Then there are no rhymes for broad in my Penguin rhyming dictionary that are spelt --oad and aren't derived from broad (/brɔːd/ according to Collins) itself. So there aren't any reasonably common words with that spelling and pronunciation in the last syllable.
Because that only eliminated words ending with broad's --oad, I tried something different -- generating lists of words containing oa and checking the pronunciation. OneLook's pattern matching dictionary fed with oa and the regex dictionary at http://www.visca.com/regexdict/ fed with
.+oa[^r].*(i.e. 1 or more characters followed by "oa" then anything other than "r" and 0 or more characters -- not perfect but a decent approximation) give rather long lists. Scanning those lists I can't find anything to suggest that broad isn't unique -- there are unfamiliar words there but they don't look like they should be pronounced --or--.Tl;dr: yes - I'm now waiting to be proved wrong.
Edit: note that some of the examples in this answer have a British English bias to them, the answer itself is unaffected