Many locations do want a long commitment, because they don't want to have to find new workampers all the time. But kind jobs are to be had.
Our longest gig anywhere so far was 3 1/2 months where we worked on the guest ranch in Colorado. The people were great, the place was beautiful, and this job paid, so it was well worth it and time flew by.
We worked/volunteered for just a couple weeks at an animal rescue, but that was because we were fed up with cleaning cat cages. On the organic farm in Florida we worked about two months, and that was about the same time we worked at the Hot Springs resort. The latter was three days on / three off, so the hours made up for it. But we noticed they are currently advertising again, and requiring the six month commitment you originally mentioned.
If you find a job that might sound good, try to negotiate the duration. It's fair to at least commit to a month. But I think two months is about the longest I would ever workamp again, unless it was a really sweet deal.
And while its not exactly a
nice thing to do, you always have the option of leaving if a workamping job doesn't work out.