What accents pronounce "quarter" as "korter"? Which other words can drop /w/ before /ɔr/ like this?

I couldn't find any information on dropping the "w" in "dwarf" (maybe it's not common in this word after all!) but I did find out after asking this question that the 2003 Harvard Dialect Survey, which involved speakers across the United States, had a question about the pronunciation of "quarter". The breakdown across the U.S. was

a. with [kw] (62.07%)
b. with [k] ("cor-ter") (30.09%)
c. I use both interchangeably (7.41%)
d. other (0.43%)
(10890 respondents)

I didn't see any geographical trends in the distribution of the different pronunciations.

I don't think I've ever heard the "w" completely elided in "dwarf", but perhaps there might be some transitional process happening, as I do sometimes hear it pronounced "do-orf" (i.e. two syllables), especially by those who have a slower pace of speech. A bit like pronouncing "film" as "fil-um".

"Quarter" is different: I pronounce it with the "w" when I'm articulating my words, and unconsciously drop the "w" when I'm talking more lazily or colloquially - though after reading your question, I'm now much more conscious of doing so!

"Quart" isn't heard much now that we're metric in Australia but I think it gets the same treatment as "quarter". I'm not aware of any other word where the "w" sound is disappearing.