Porch Swing hardware

Hi all,
I just found this group...looks to be very informative.
I am looking for a specific piece of hrdwr for a porch swing. Rather than a chain assembly, this is more mechanical...almost like glider hrdwr. I've looked and looked and can't seem to get anywhere. Has anybody else ever seen something like this? Do you know any good places to look for hard to find, weird stuff? Thanks in advance.
Jamie Charlotte, NC
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